I mostly play computer games now. I used to play for hours, like all day on PS2. But now I play on the computer, and I listen to audio sermons while playing solitare or majong (spelling?). My brain takes in the messages from the sermons and plays the games almost automatically. When I need to stop to take notes, I use either wordpad or I pause the mp3 and write them down in my notebook. For me, it's a great way to get in the message and keep my hands busy too.
I guess some people may play more, some less. It's so easy to get into another 'world' with games. It's probably different for all of us.
The best way for self control that I'd suggest, I guess, is limit yourself to so many hours. If it's a game you have to save periodically, and say, it's been an hour for example, and you've set your limit for an hour, then tell yourself "when I get to the save spot, I quit".
You are right, obsession is easy. I fell deep into it a long while back, and became so obsessed that it ruined a relationship/friendship of mine.
If you feel yourself becoming obsessed at all, shut the game off, unplug it, and choose a new hobby for a while. In the meantime, get something better on your mind. If you like listening to things, I think there's a website somewhere with free mp3's of the Bible. It helped me. It might help you too. I dunno.
I hope this helps.