Mastery is a big one. Getting better at something feels good, even useless things. This ties into "progress", which is what a lot of games are doing to give us

Mastery is a big one. Getting better at something feels good, even useless things. This ties into "progress", which is what a lot of games are doing to give us a false sense of mastery (collect the things, get the rote achievements, etc). I've also played for pure adrenaline sometimes - a bout of CounterStrike before my AM classes helped wake me up back at university, better than coffee, but not as good as finding a spider in the room. There is also some chatter that gaming can be a form of self medication for ADHD and related disorders. I haven't tried getting a diagnosis, but it runs in my immediate family, and I definitely feel like I sometimes game for a bit to "get it out of my system" and settle my mind to focus on other things.