They also took out kudos challenges where you perform drifts or 366s between cones. Instead they replaced it with the worst feature yet, the Cone sprints. This is the worst event ever invented in PGR to date. There's also a limit on how many kudos you can earn during a race, absurd. Some challenges you have to earn a certain amount of stars, but once you reach the 5 star limit, you have to stop your combo so the star meter can start again.
PGR4 has a horrible online feature. Once you do manage to find a game, you can't even tell how far along the match is. So once you join you have no idea if the people have just started to race or if they are on the last lap.
Small text. Only play this game if you have a large HD TV because if you don't you will need a magnifying glass to read the text on screen. Some screens even have white words on a white background!
Bikes. In my opinion bikes should have been left out. They are difficult to handle and you can wreck real easy if you hit another car.
Damage modeling. If I smash my car into a barrier at 180 mph I want to SEE IT! In PGR4 your car will still look almost brand new.
The sound and handling of the cars is improved. The weather can add variety to some races, but usually its just annoying and you'll lose most control of your vehicle when you hit a puddle or snow patch.
I know I'm missing some other stuff but these are the main complaints I have with this game. Bizarre Studios had a long time to make this game unlike the rushed PGR3 and came up with the worst iteration of the series yet. Its sad to see such a great series come to this, especially since PGR2 was one of my most played XBOX LIve games in the past few years.