Yes, they're different from Pro Street, but doesn't mean they're any better than it, or than they're not worse than the previously released NFS titles. I have played all NFSs since The Need for Speed released by Road&Track, actually I have most of them installed on my PC right now (apart from NFSC, NFSPS and NFSUC, which I uninstalled because I couldn't stand them).
For me, the worst NFS ever made was Pro Street. Not because of the events, graphics, customization or anything else (even though everything could've been much better), but mainly because of the physics. It's ridiculous. It's neither arcade or simulation, it's a weird combination of boat racing with airplanes, grip where it's not supposed to be and cars not turning when they are supposed to. It's not fun. It's like I'm not driving a car. And the car cameras made it even worse. The soundtrack isn't so bad, but the way they have implemented it in the game made it look terrible. Playing NFS Pro Street gives me headache.
NFS Carbon wasn't that bad, but NFS Undercover screwed things up again, even though it wasn't as bad as Pro Street, EA Games compensated this by adding up plenty of bugs.
NFS Undercover has several graphical and physics bugs. As examples I can say the sun light passing through bridges and completely pixelated shadows as distance goes by... Every shadow's "pixel size" might go up to 32x32 in the track. A friend of mine had taken some pictures of it, and I even uploaded it here, I'll check my attachments to see if I can find it. [edit] Here is it. [/edit] UC's car handling is not as bad as Pro Street, but it's still not fun or any realistic. NFS Carbon's handling is terribly bad too, although Pro Street's physics managed to be a lot worse than both UC and Carbon together.