I picked up PGR4, and here are my thoughts on it:

- It's fun.

- It's fun.

- It's sexy.

- Achievements are pretty easy to get.

- Nice selection of cars, unfortunately the DeLorean doesn't travel through time.

- Sound/Music are pretty good.

- Geometry Wars Waves is pretty fun, but nowhere close to Retro Evolved.

And that pretty much sums up my thoughts on it. Check it out, it's a cool game.