Got to spend some quality time with this tonight. I'm liking how they've sprinkled the cars throughout the game world, and you have to explore to find them. Once you find one, you can warp back to it any time you're free roaming and don't have cops after you.
I found a Corvette ZR-1 early on that's proven to be the best all-around car I've encountered so far, and I've apparently found half the cars. It's funny, because I thought the ZR-1 had horrible handling in Need For Speed: Hot Pursuit, but I like it a lot in this one.
Every scoreable item in the game has its own speedwall, which gets superimposed on the game world when you get near it. Really slick.
Each car does have its own set of races to complete, but those races are shared across multiple cars. I also had an ambush event once, where I had to lose the cops within a set time limit. Losing the cops works pretty much like Interceptor mode in NFS:HP.
The game world is a good size, but not gigantic. Free roaming is fun, because speed and traffic violations can get the cops after you for ad hoc pursuits, complete with roadblocks and spike strips. Between that and all the other activities and exploration, you always feel like your free roaming time has a purpose.
I'm enjoying it.