I still think NFS Undergound 2 is the best in the series.
Most Wanted is a close second, but I think the cops were a bit odd on it... overly agressive and persistant at a high heat level yet ridiculously hard to keep them on your tail at low heat levels.
Carbon, ProStreet and Undercover all suffer from the EA symptom of "well it's not broken but let's screw with such'n'such game aspect anyway"
I used to love drift racing in NFSU2 was just such a joy, then it became so crap in all the games that followed; and god knows how but they totally screwed up even standard driving in ProStreet.
Add to this the whole "real-action cutscenes that play out like extremely bad made-for-tv-movie cop shows", I mean ffs The Fast and the Furious was a cool movie, 2 Fast 2 Furious was attrocious, and the ending to Tokyo Drift made no sense.
You know what would've been a good story for them to play with and that's the Gone in 60 Seconds one... it's not involved enough as to distract from the game, while no so bad you cringe each time you'd see a cut-scene.
Also I think it's just way to damn easy to get parts in the game, like you get far enough and you get stupid money. Add to this I don't think the whole cop aspect works... EVER.
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