I will only re-buy a game if its something I really love or if there are new features such as online play. I don't really care about achievements at all, but I like friends leaderboards.
I am kind of sick of crap early 80's arcade games that are out now. I could care less about Frogger or Scramble or whatever else is out there. Give me late 80's-90's stuff and I'll buy if the options are right. Seeing Doom on arcade was a wonderful suprise, too.A Live-enabled version of Tetris Attack would be the end of me, for sure. Also, GI Joe arcade with co-op would be sweet.
I have all of these games(and mostly everything else) for my PC. I can play most of them online to a degree with friends via Mame 32k or ZSNES, but they are a pain to set up and lag out sometimes. I will gladly pay for convienence if Microsoft brings out the games I want to play.

