From a personal taste standpoint I think this series has gone too far beyond an actual racing game to be quite honest.
It has become a typical case of style over substance.
A lot of my gripes come from a purely technical stand though, rather than from decisions made toward gameplay.

Driving skill has taken a serious backseat in revenge, and not just thanks to the overly crash-centric game play found since B3 (I'm talking outside of crash mode).
No longer is it about ovoiding the other cars on the road, especially as you can now happily mash into almost anything driving in the same direction as yourself, it has become more about fighting an overly cluttered grapical nightmare to tell where the hell the road actually goes.
In SD the resolution is nowhere near sufficient to tell what is going on far enough up the road to actively prepare for it given the speeds at which things move in this game.
It's not that the game looks bad, quite the opposite. There is just too much lighting/blurring/roadside-detail fanciness for standard definition (coupled with the ps2's aliasing) to cope with.
It actually looks pretty good for a last gen game, as long as you don't try and actually play it..

And you better like loading screens, I mean really like 'em.. a lot!
When just restarting a race takes you back to the load screen and you're trying a difficult burning lap they get old pretty fast.
While I'm being picky changing the camera gets annoying too since you have to do that everytime a race starts, or restarts, if you prefer to play inside the car/bumper cam.
A "quickrace" option would have been nice too as would an auto-loading save file I don't have to choose every time so I could start the game up skip the logos and intros and be racing inside of five mins.

Aside from these annoyances I don't feel it's greatly above average to begin with, there isn't really anyhting it does better than the previous burnout games.
The racing mode, or missions as they're laid out here, isn't as good as B3 which in turn wasn't as good as the second or first.
Crash mode also wasn't quite as fun, even if in B3 it kinda degenerated into being totally about the multiplier icon.
After I gave a less than favourable review of 3 (although for mainly different reasons) I think I'm done with this series. a shame since I really ejoyed the first and second titles.