PGR4 really isn't that much different from PGR3; the jump from PGR3 to PGR4 is so minor compared to the ones from MSR to PGR, PGR1 to PGR2, or PGR2 to PGR3. It actually feels more like an expansion pack than a sequel.
The PGR series is still my favorite racing game series (PGR2 is the best) and I can only hope that Activision doesn't ruin the next racer Bizarre does.
And I just realized that developers that make racing games usually end up making good shooters. BothThe Club and Black were awesome. Microsoft should get Turn 10 off of Forza 3 and get them on a new shooter or something.