Yeah I had a whole rant about MW
In the first NFS Underground you at least got rewarded for skilled driving and manoeuvres. In Underground 2 they removed a lot of those elements and they changed the reward from the useful unlocking points to N2O. You practically never run out of N2O, instead of it refilling after each lap, now it slowly refills if you maintain a certain speed or if you pull off other moves (near-miss, drift, etc.) And finally in Most Wanted, now you actually get rewarded for crashing, destroying, and all sorts of crappy driving (you get bounty points).
The cars and the graphics were great, but the game felt like EA was trying to catch on the 'criminal' element of games like GTA, True Crime, etc. except in a racing game. It just became chaotic, and you have no incentive to drive with skill! The only possible reward for a drift, a near-miss, or a clean turn is more stupid N2O which I barely use anyway!
Besides the concept and game mechanics being faulty, there was the permanent daylight. In the Underground series one of the biggest complaints was that it was always night, and there was no real environmental change unlike all the previous NFS games (you could choose what time of the day you wanted to race, and which sort of weather conditions). In MW they made it daytime, but now there's no NIGHT!! WTF?! It's one or the other??
Either way, MW was not a big leap from Underground 2. If you had Underground 2 you'd be pretty disappointed if you spent the extra cash on MW, unless you're a huge fan and collector of the series.
Underground 1 is by far my favourite from the NFS tuner series.