Horizontal growth vs Vertical growth.

The biggest reason is probably because vertical growth tends to increase challenge and difficulty, providing a feeling of progress for the player.

Developing horizontal growth too much also means you're spending resources on features that may not be used or even liked by players. What's better, making a game that takes ten hours to play through, or a two hour game that allows five variations to pass each challenge? It's more open, and might even be more satisfying, but your players are still going to feel they only got 2-4 hours out of it. I also recall something about a Rock Star designer regretting making GTA IV so large, because most players were ignoring something like over half the content. (In event completion, not just acreage or activities.)

It also becomes more cumbersome to test, making sure that players can reasonably pass each section no matter what "horizontal" option(s) they've invested in. If the player has made it halfway through the game relying solely on technique B & C, is it "fair" to insist they halt their progress to perfect technique A just because they're stuck at a challenge that strongly benefits from it? Sure, proper design should neutralize this, but that still takes more time and testing to verify and adjust for.

I'm not discouraging horizontal growth - I love replaying games with different focuses, or having the freedom to do things "my way." But developing it does come with its own costs.

Gaming is about learning. With this in mind "horizontal progress" is by far the most important aspect of a game, because the player needs to learn and practise new skills. On the other hand "vertical progress" is almost without any value.

You must be careful to not see other "gaming effects" as "vertical progress". Take a look at your classic WoW game. Your character has lot of vertical progress, but there're other effects which keep the player to get back and go on (i.e. learning new talents which introduce other playing styles(player need to learn), gain better gear (collecting aspect), raids(social),crafting(economy),battleground(competition)).

Many game with mostly vertical progress (you got fireball1, .... fireball10) only survive the first half hour if they introduce some other aspect (visual changing environment, other opponents with other behaviors etc.) .

"Vertical progress" is much cheaper to develop, it often can be done by an equation multiplying an enemy's stats to get a higher level enemy, or linearly reducing time or resources available to achieve an objective. But I wouldn't say "horizontal progress" is rare in games - it depends what type of games you are looking at. The Zelda series is a clear example - the different tools acquired by Link as the game progresses allow different types of puzzles to be solved. Many MMOs, although their vertical progress is more obvious, also have horizontal progress in that the character learns a wider variety of spells or abilities. In some cases characters become able to add a secondary class or additional professions, and able to gain new modes of travel like swimming and flying which unlock new locations.

Horizontal progress isn't inherently better than vertical progress because it is easy to do badly - if you have two attacks that have basically the same cost and same effect that doesn't add anything to the game.

The biggest reason is probably because vertical growth tends to increase challenge and difficulty, providing a feeling of progress for the player.

I agree that vertical growth provides a form of progress, which can be a reason to play. But it is a rather weak reason.

I argue that vertical growth rarely produces increased challenge or difficulty on it's own. In Nethack, most player deaths occur during the first ten levels, and after that the player rarely dies. In Borderlands, one of the toughest fights is around level 15 against a cave full of alpha skags. Both of these examples point to balance issues as the main source of challenge or difficulty, and even suggest that a perfectly balanced game might be a boring slog of more of the same with bigger numbers.

Horizontal growth can enhance complexity. Having six spells is tricky business if they are to be used in a high-speed fight. Handling the welfare and purpose of a dozen planets can be mind boggling if they are detailed worlds.And this gets to a different kind of balance issue, where complexity is at once both desired for it's additional features and despised for it's propensity to overload the brain.

The purpose of vertical growth is progress. It gives the player the thrill and reward.
The purpose of horizontal growth is learning. It hides some complexity from a new player.

So, horizontal growth (in properly designed game) has nothing to do with game experience but only with the pace at which human brain can comprehend new things.

Most games employ a mixture of Vertical and Horizontal growths to players as they advance through the game. However, I find that the focus is almost always on the Vertical growth and not much of the Horizontal growth.

Agreed. Perhaps a problem of horizontal growth is that it requires (as other people noted) consistently more content. Different challanges. In some tabletop games, this is very apparent (perhaps even more than in video games). Horizontal growth increases your minimal score - but I never managed to win by having more options. Simply put, they rarely have the necessary range of challenges to make "multiple options" a good alternative over "get a boatload of benefits by doing X".

As the game goes on, specializations complement each other.

While I think the multiple options should be made more valuable, I see many difficulties in making this happen.

AngleWyrm, that quote was in response to "(why) vertical growth is the more common technique in games as the primary focus for advancement" - The "biggest reason" is it's fundamentally cheaper and easier compared to the hard work involved in the alternative.

Maybe I've misunderstood Zummy's post, and we all agree bad design of any kind is going to result in a bad experience, so let's remove the discussion of quality for now. My impression was about the opportunities for a player to alter their experience, developing laterally or adjusting the style of play to suit them rather than using a "different set of numbers." The way I see it, having choices or new abilities are not necessarily horizontal advancement if the game's design limits their implementation.

Gaming is about learning. With this in mind "horizontal progress" is by far the most important aspect of a game, because the player needs to learn and practise new skills. On the other hand "vertical progress" is almost without any value.

You must be careful to not see other "gaming effects" as "vertical progress". Take a look at your classic WoW game. Your character has lot of vertical progress, but there're other effects which keep the player to get back and go on (i.e. learning new talents which introduce other playing styles(player need to learn), gain better gear (collecting aspect), raids(social),crafting(economy),battleground(competition)).

Many game with mostly vertical progress (you got fireball1, .... fireball10) only survive the first half hour if they introduce some other aspect (visual changing environment, other opponents with other behaviors etc.) .

"Vertical games" do not not mean they're limited, or strictly linear. They do still include learning, steadily improving your skill in those core abilities. You're right that we shouldn't be misled into thinking "gaming effects" are vertical progress, but the same applies to mistaking trickery for horizontal progress too. The illusion of choice is often finely crafted to trap you into doing the same darned thing, but making you think it was your idea in the first place.

While World of Warcraft's premise might seem horizontal, it seems more like an open ended vertical that resolves the same way whether your character is swinging a broadsword or throwing a fireball. I realize there's a few exceptions like social and PVP but the bulk of the game plays out identically without offering the player a chance to come up with their own solutions or to changing the game's pace. Once you're near the end of the game too, your character becomes strictly defined only by the level of vertical progress you've made, plus or minus the contents of your immediate group. More than half of your learned abilities are either obsolete or pigeonholed into the "only" viable strategy that every other player must use to be effective. Skill points seem to give a certain level of freedom, but most of the later content has been designed with specialization in mind. Player originality is dropped in favor of strict developer designed roles, and points invested in skills outside that role are virtually wasted.

I see horizontal as games offering multiple distinct paths for progression. Mount & Blade can be conquered through direct warfare, or you can use politics and management to expand your kingdom and have others pick up the slack for you in crucial battles. Civilization offers players other ways to win than just by eliminating everyone else. Diplomacy, industry, and influence are equally viable, and you may need to change your intent based on game events. The Commandos series lets you use any combination of skills and preferences to get through - you might focus on evasion and subterfuge, misdirecting guards and carefully sneaking everyone through the cracks. A strategist might prefer stealth eliminations to create openings in the enemy line without alerting reinforcements. Or just outfit your squad with scavenged weapons and overwhelm the whole garrison by force. In these games you're free to develop the strategy you like with the skills you prefer, that all play out quite differently without being told by the design, "No, you cannot play like that."

Sunandshadow brought up the Zelda games: While it's a very well designed series I don't think I could label it particularly horizontal. Most of the time when you're collecting a new tool it's not to give you more options but only as the means to pass the next specific obstacle. Four unlit torches beside a locked door means you'll need a fire to light them. A cracked wall always needs to be broken. The hookshot will cross that chasm with the switch that's out of reach. The player is doing little more than identifying a specific situation and using the sole working solution. It certainly does prove your point that a well designed vertical experience is much more satisfying than a variety of badly designed choices, and also that a game's experience can't be dismissed solely on its design philosophy.

Of course, maybe I've completely missed the point of the discussion, but hopefully that at least clears up the way I see the design.

The tabletop RPG Mage: The Awakening (by White Wolf) ties the two in together. As a character gains more ranks in a particular sphere of magic their effectiveness at casting un-memorized spells from that sphere increases. Each rank also brings new abilities as well.

For example, the death sphere (might be a bit inaccurate, going from memory):
Rank 1 - you can see auras of death
Rank 2 - you can shield yourself with death magic and talk to ghosts
Rank 3 - you can hurt people with death magic and raise zombies
Rank 4 - you can "resurrect" people as undead revenants
Rank 5 - you can summon ghosts from the underworld and steal the lifespan of mortals

As your powers increase more options to approach a situation present themselves.

The tabletop RPG Mage: The Awakening (by White Wolf) ties the two in together. As a character gains more ranks in a particular sphere of magic their effectiveness at casting un-memorized spells from that sphere increases. Each rank also brings new abilities as well.

For example, the death sphere (might be a bit inaccurate, going from memory):
Rank 1 - you can see auras of death
Rank 2 - you can shield yourself with death magic and talk to ghosts
Rank 3 - you can hurt people with death magic and raise zombies
Rank 4 - you can "resurrect" people as undead revenants
Rank 5 - you can summon ghosts from the underworld and steal the lifespan of mortals

As your powers increase more options to approach a situation present themselves.

As far as I remember it is also the way of Vampire: Bloodlines (from White Wolf as well). I believe it is a great approach though it may be confusing for some at first as it is not fully apparent whether the new abilities are replacements or additional options. I am also considering to develop a new system that has both options to gain mastery/specialization and learning new skills. Maybe with a clever "synergy factor" it could be achieved to inspire players to go with a healthy balance of specializing and learning a set of "active" skills. It may be a good idea to consider that some players prefer to play more aggressively - with preferance to active skills, and some just like to sit back and watch - probably prefering the passive skills.

Vertical growth is what I feel ruins most PVP based MMORPGs. The individual gains too much power thus throwing off the balance of combat. "He hits for 1,000! I only hit for 750!" Compare this to lower level combat where someone would be hitting for 100 and someone would be hitting for 75. That is a tremendous difference in damage per hit at higher levels. I just can't fathom how hard it is to comprehend exponentially increasing power of a player ruins balance if the power is not kept in check.

Granted, the balancing of other statistics is also key, namely hit points. Lower the power curve(vertical) for games involving PVP while providing more play options(horizontal).