I've only tries a few games. My experiences:
- South Park: Runs flawlessly
- Dirt 3: Some people said it would run fine. This is my experience: http://xboxdvr.com/gamer/Gaschman/video/12698282
- Castle Crashers: Perfect
- Pinball FX: I didn't notice any differences compared to the 360 version
- CoJ Gunslinger: Terrible framerate, input delay
- Banjo Kazooie: Perfect
- Banjo Tooie: Perfect
- Banjo Kazooie Nuts and Bolts: Framerate worse compared to 360 version
- Battleblock Theater: Perfect
- Super Meat Boy Perfect
Also: Lode Runner doesn't show up in my ready to install list.
Just to test it out, I tried Stick of Truth really quick from the beginning. Played through probably 20 minutes, it was great.