Definitely been there, done that.
NFS Undercover is basically Most Wanted but somewhat recycled. When I say recycled I mean that there was and entire section of the map that was ripped directly out of Most Wanted and littered with palm trees and beach houses to make it look original. I am not exaggerating. It was the SAME section of track from Camden Beach. That is my only real gripe with the game. This in no way spoils the gaming experience for anyone and I can't see it being a problem for people who just want to enjoy some racing with the revamped driving engine.
Story: You play as an undercover cop who gets sent to bust some punks stealing cars from the docks. The cut scenes are fine and you get a clear picture of where the plot is going. The acting is as lame as any other NFS game and none of the characters seem smart enough to be able to steal shipments of exotic cars under the radar. 7.5/10.
Control: This is where the game shines of the other NFS games. In Undercover, the handling has been redone so that you can drift your way around corners, pull off 180's and 360' with the touch of a button. This makes you feel like a real wheelman and evading cops is much more fun this way. 9/10.
Graphics: Lots of aliasing. but when was the last time we had an NFS game without aliasing issues? The cars look great, the pavement shines like in Underground, and the sense of speed is definitely there. 8/10
You can go on and on about Undercover's pros and cons, but it's a fun racer that you can relax and play. There's a great deal of content and a strong car list here. If the price of 39.99 doesn't suit you, then wait until it drops to 20 like Pro Street and pick it up then. This isn't a must-play but it will keep you occupied for a while. 8.5/10