With NFS:U, EA has really hit the sweet spot between arcade racer (e.g. Ridge Racer) and sim-heavy driving games (e.g. Gran Tourismo). This game successfully taps into the "less than legal" street racing/car-modding scene made popular by recent films like Fast and the Furious!
Add to that an online competition & ranking component (4 player PS2 or PC together!) that is almost as simple as Battle.net and EA has got itself an explosive mix!
The graphics are excellent, especially the "focus" effect while using NOS is really cool! The sensation of speed is absolutely amazing (unlike other racing games where the only way you knew you were going "fast" was by reading the speedometer)! The Dolby ProLogic II sound is great too!
The _only_ complaints I have about this game is the lack of USB keyboard support (forget about chatting on PS2 platform unless you're a patient person) and there's no racing for pink-slips online! But those can wait for the next version! Oh yeah, maybe adding some cops to outrun would be fun too!