Weird, the reviewers didn't have any problems with the framrate and neither did the posters in this thread who played it before release. Now everyone seems to be having issues with it though oO.
Framerate is awesome on 360. I noticed one slowdown during some weird physics effect (the monster's parts flying to the air, while fighting 20+mobs, with smoke and fire present), but the overall experience is extremely smooth. It helps that my PC is crap, I run it with 30fps framecap and on 1280*800 to not overstress my old pc parts Compared to that ,this is HEAVEN.