Mass Effect 1 is still one of my favs this gen. Emulators for last gen games will come through if you create a free account and start up online. That opens up Kotor 1 and 2, Ninja Gaiden Black if you haven't done Sigma 1 on PS3, Jade Empire, Halo 1 and 2 although you're better off looking for Anniversary cheap with the graphics upgrade. ESIII Morrowind was a big wrpg but load times and visuals are pretty awful really. Fable The Lost Chapters had maybe 5-6 hrs of extra content over the original release but will be hard to find. Same deal on load times. Can't recommend Gears Judgement, maybe when it hits $30. Halo Reach lacked the chief but had a decent campaign.
This link seems to list everything that was ever exclusive at launch as well as what's also on PC.
http://en.wikipedia.org/wiki/List_of_video_game_exclusives_(seventh_generation)#Xbox_360
