The speed camera flashes.
The AI, they try to ram you more than they care about winning.
The game constantly sets you up for crashes.
I had a race where the route was through a couple of repair station, WTF, my car changed colors every time through it, messed my concentration up.
The inconsistent handling of the cars, modded parts or not.
Cops in races.
The races aren't closed track but yet you have to drive a certain path or you'll miss a checkpoint causing you to lose the race, the AI will knock you off the route sometimes too.
Having to constantly look at the map while racing.
I'm not sure about this one, having to drive miles to each new race. Is there a quick travel option for the first time you do a race?
The soundtrack sucks, yea, I know it's a subjective thing but still.