Well, apart from the game once removing all buttons while viewing a replay (I had to call task manager to finish process), I've never had a problem with NFS Shift since I first installed it. And I'm not using default graphics options, I always change everything (to maximum) when I first open the game. Oh, and, of course, aside the physics bugs (which are exactly the same as GTR's, GTR2's and GTR Evolution ones).
I like the game, it finally seems to be playable now. BUT: Tuning is terrible, car customization has never got so bad in a NFS, you can't see the interiors or anything you're going to install BEFORE installing it and going to a race, there's no showroom to see your car, vinyl customization now takes much more time and it's also much more restricted than before, which means much more boring to create your own vinyls. Some things are also slower to load than on previous NFS's, i.e: cars take quite a while more to show up when you select them.