It is like Shift's physics, but they aren't terrible. You HAVE to know how to tune in order to get the most fun out of the game. The default settings on the control settings and all the cars need work, so be prepared to get frustrated with some career events. When you are tuning, the live telemetry is a godsend since you'll know a lot more about what the car is doing than in GT5. A wheel is recommended, but not required.
Online, it's no where near GT5. Online lobbies have to tuning feature, voting, kicking feature, or a way to filter assists. On top of that, the location/collision detection is pretty bad depending on lag. You see where when two cars collide, one car may be affected instead of both cars, and neither cars would have to touch in some cases.
Even with all the flaws, you STILL should pick it up. Don't expect a poor man's Forza or GT5 because you'll leave yourself disappointed. This game isn't about taking stock cars on sport hard tires on Nords. This game is about building cars and enjoying the racing against opponents.