I used to own a 360 as well as PS3 and besides playing mass effect and a couple of XBLA exclusive games I never played it. My subscription fee went to waste and it just gathered dust. Left 4 dead was fun, but got old after about a month as there wasn't really much of a leveling system or unlocks or anything.
Forza maybe? I guess thats really the only 360 game I havent played that I wish was multiplatform.
There are lots of games in PC that I would like to play. My current laptop has no balls and cant really run anything more taxing than solitaire.
I really wish Titanfall was coming to PS4, but so far thats the only exclusive I'm a bit jealous of. Respawn is a brand new company and said that they between getting up and running and working with new hardware they wanted to focus on a single platform. I am willing to bet that any sequels will be on PS4 as well as 360.