Well, first of all, I want to say one word about the sound. I was a bit harsh, it get's better. Not 100% lifelike, but better than it was when I wrote the FL.
Regarding the graphics I think that the graphics of both NFSUG and NFSUG2 is better than FlatOut. This is due to the ambiance it creates and the high sensation of speed it gives. Although, after playing a while I do feel that the blurring etc. actually was a bit better in the first one than this version.
But if you maxout the graphics in this game the lightning, reflections and highres cars puts flatput to rest. But that's just my oppinion.