For me it's atmosphere
Some of my favorite games like COD WAW, Halo Reach, and Battlefield 1 have amazing atmospheres that take them beyond being amazing games to me, they make them special to me. Atmosphere is the #1 thing that draws me into a game beyond the basic things like gameplay.
When I think of the best example of atmosphere, I think of Battlefield 1 first. Both its campaign and multiplayer have amazing atmospheres, but for this, it'll be easier to explain the multiplayer side of it. Do note, it can be hard to fully understand the atmosphere being described because sometimes you don't have the full context of the event, which may span as much as hours or days beforehand, but I'll try my best to explain it.
Video I took a few weeks ago, that I'll describe my feelings on: www.youtube.com/watch?v=2zPWy2vHgaA
It's at the end of the round with the end music blasting, compared to the usual state of it being more in the background/not there at all. We only have 2 spawns left to defeat the enemy and take the last objective. Just as we take objective B, we start to lose objective A. Just a split second longer for them to start taking objective A and we would have won. Now we have 0 spawns left(but due to a special rule, as long as we are capturing the last objective we can still spawn). It's a fierce fight for the last objective, whoever captures it first wins the game. I die in the fight for objective A and wait for respawn. My stress is now really high as it's anyone's game now. We lose objective A (They are more than 50% of the way to capturing it) and now our team can't spawn there. I can now spawn, and so I spawn at objective B.
I spawn in to see a towering gun turning to fire on objective A with soldiers around me rushing up the hill and into the trenches to take back objective A before it's too late. The enemy's progress on capturing the objective inches closer, just adding to my stress. Explosions and bullets fire around me as I run to stop the enemy. I pause to fire my grenades at the enemy position in desperation to stop them. The tides begin to turn as we start to capture the objective. I arrive to put my weight into capturing the objective, laying down suppressive fire to anyone who dares to peak into my firing line. I watch as the capture progress goes up and up until it reaches 100%. We have won, the music finally relieves its added tension, and the camera zooms out to show the entire battlefield.
During that entire time I forgot about everything else besides that game, my full attention was to winning that hill and the game. The combination of music, looks, sound, and action of the game had me captivated.
It's almost only games like these that have atmospheres so strong and captivating that get me into this state. Whether it be from an action-packed atmosphere like Battlefield 1, a sorrowful one like Halo Reach's campaign, or a mix of both like COD WAW's campaign.
