Alright, I beat the career mode of it yesterday and am at 66% of "game completion". It took just under 15 hrs to complete the career mode. So that's a bit disappointing since it took about 40hrs to complete the career mode in Midnight Club LA, although it's MUCH more non-linear.

The issues I have with NFS:UC:
1) The game is very easy. It never really gets difficult, although I think getting the last 1/3rd of the game may take as long as the first 2/3rds, since it's at a higher level.

2) The game is entirely linear. As other reviewers have pointed out, the "open world" concept is pointless in this game. That being said, this game is basically Most Wanted 2. You do some races, you avoid some cops, you beat a boss, you move on.

3) The environments are lifeless and boring. The roads constantly have this sheen on them like they are wet, but they aren't, and you can tell it's being done just to reflect the sunlight to "look impressive". It gets old really fast.

4) There is some SERIOUS slowdown issues in the game. To the point where I actually started getting annoyed by it during a couple of races. When you have a group of racers ahead of you (which doesn't happen very often unless you suck) and you're smashing into things, all the data on the screen brings the thing down.

What I like about the game:
1) As I said above, it's basically Most Wanted 2. If you loved Most Wanted you'll probably love this game. The cars handle about the same, the cops react the same way, the flow of the game is the same.

2) The graphics aren't bad despite the slowdowns. There's no night racing which is a real letdown, and all the races happen at either sunrise or sunset (and seriously, how many street races take place at sunrise or sunset??) and so the sun will be glaring at you quite often.

3) The sense of speed is INTENSE. The game is worth playing just to get the Bugatti Veyron. I can't even explain how fast it is. It's like driving a missle.

4) The types of races are a lot of fun. One of the most fun they have is "Highway Battle" where you have to get 1000ft in front of your competitor in less than a minute while ripping down a highway at high speeds and trying to avoid traffic.

Overall I've had a good amount of fun with this game. It won't provide me nearly as many hours of enjoyment as MC:LA but it's certainly a fun game to play. I totally disagree with any review that puts this below a 5/10.

I haven't spent any time playing it online.

If you're a fan of Most Wanted you really should play this game. It feels dated compared to other modern racing games, but it's still worth playing. It's probably not worth $60 to buy given the short amount of time necessary to beat it and non-replayability but it's certainly worth a 7 day rental.

Overall I give it a 6.5/10.

For reference I'd give these scores to these similar games:
Midnight Club Los Angeles: 7.5/10
Test Drive Unlimited: 9/10
Burnout Paradise: 7/10
Need For Speed Most Wanted: 8/10
Need For Speed Carbon: 7/10