What kind of game to create if you want "decent" money out of it?

As an indie your best bet really is the casual/social market, you stand a much better chance competing against games like angry birds or farmville than you do competing against Starcraft, Left 4 Dead and Mass Effect.

Now it all depends on what you consider "decent" money though. If you want to make millions then you're in the wrong field, indie game developers don't become rich unless they're insanely lucky and good but making a living is perfectly possible if you work hard. (As you build up a code and fanbase it will become easier but you should be prepared to have to put in 50-60 hour weeks to make ends meet on your first few games)

One approach to making good money in the indie market that has emerged with the mobile revolution is producing lots of small games. Rather making 1 game over 2 years in hopes that it turns a decent profit. You invest your resources in reusable frameworks and assets and launch a new game every month or 2. if you produce 6 small games a year sell them $4 each then you can make a good returns off a fan base of only a 5000 people. If you produce fun well polished games then most of your fan base will buy the next game you release especially if the has small price tag. Producing a lot of small games also should gradually increase your fan base and new fans may buy items from your back catalogue. Also it increases your chance of getting a smash hit.

Also it worth noting that smash hit indie games are virtually never a for a first game.

Rovio who make Angry Birds probably one of the best know successful indie companies had been in business for over 6 years and released 51 games before angry birds.
Angry Birds itself initially cost [font=arial, sans-serif][size=1]€[/font]100,000 to make but then its also generates over [font=arial, sans-serif][size=1]€[/font]50,000,000 in revenue. Even then the game was a flop for the first 3 months after is was released.

I'd aim for turning out lots of fun polished games that turn a profit and hope that ones becomes a smash hit.

...

Somebody plzz tell me which languages are the best for learners [...]

I agree with making several smaller games per year. You have to also think about the development time/risk.

You keep mentioning MMOs or games that would take years to complete... but that isn't really a realistic approach for an indie developer. Instead of trying to make a blockbuster game that will make you millions, aim for making 2 games a year that might net you $50k each in sales.

That's not all that outrageous considering you'd need less than 17,000 sales of a $2.99 game to hit that mark. That's totally possible with a small indie game that is semi-decent. You also need to consider that these games will continue making you money for years. The more games in your library, the more chances to make money.

I'd rather have 10 games made over the course of 5 years than 1 MMO made in 5 years that may or may not even do well. It's likely that 1 of those 10 games will do really well, a couple will do decently, and the rest will just bring in small bits of extra money that add up over time.

I guess the lesson to take away from this is to just not put all of your eggs in one basket. Also it's far easier to finish a small game as an indie than to finish a large scale, multi-year project.

...and to repeat myself again, no one (other than myself, in an aside where I specifically mentioned quick throw-away games as an alternative approach for those with less time available) who has mentioned smaller games has said they shouldn't be polished, fun games that are made an marketed to the absolute best of your ability.

You're disagreeing with something people aren't actually saying. We all AGREE that your games should be as good as you're able to make them - we're just suggesting that is probably a more achievable goal if the games are smaller.

It's not good to spend too much time working on your GDD as the game design should and will change during development. The artists and programmers on the team will have ideas and those will turn into parts of the design. Technical hurdles will be hit that requiring watering down aspects or abandoning features. The Testers will find parts that don't work well and concepts that are small but are also the most fun that may requiring potentially large changes to the game design.

But glhf has no use for that kind of flawed and wasteful production process. He has made it clear that he's going to produce a perfect GDD that requires no alteration after the fact, then recruit skilled programmers, artists and project managers willing to work for a share of the inevitable future profits (presumably convinced by the obvious strength of the GDD). And then, as long as the peons will execute the GDD faithfully, the result will be a quality game.