The first thing you'll notice, and most impressive, is the graphics - there are some very impressive lighting effects and detail on the cars. The environments are a little lacking in comparison to console versions, but that should be expected. Textures are a bit on the blurry side and it's easy to tell where corners were cut with geometric detail on the countryside roads. the draw distance is simply amazing for a handheld though. You can see buildings miles in the distance and easily tell where you are in the game's world. It could run a little bit better, playing multi-car races with traffic makes the game slow down and chug a bit.
On the topic of traffic, it's mostly missing in this version. at most you may see 2-3 cars on the road at any moment. The world feels emptier than it should for it, and the races lose some of the hectic, traffic avoiding pace.
Most importantly, almost all the content from the PS3/360/PC versions are in this port, and as far as portable racing goes, it doesn't get any better at this time. There is also the same online free-roam multiplayer, but it's limited to 4 players - probably a good thing considering my experience was fun, but collisions with other players were unreliable and often resulted in cars jumping and teleporting all over the road, or suddenly being on top of your car when you try to take them down.
It's hard to complain too much, considering what has been squeezed into this port of the game, but it does clearly fall short of the console experience in some ways. If you would prefer to play the short, single player races when away from home, this is a great vita game - the races never take too long and it's easy to spend a lot of time unlocking everything. If you're just looking for a version of this game to play, go with the console or pc versions.