In my opinion, the biggest problem that needs to be fixed is the fact that some (or possibly ALL) cars are problematic with regards to tuning. I made a post about this in the tuning section's "premium upgrades" thread, but basically, when making tuning adjustments to my evo X in an attempt to combat the attrocious understeer that it has (which is completely unrealistic, BTW), I noticed that no matter what I do to the settings, nothing changes the behavior of the car.
Suspension settings, center diff settings, lsd settings... nothing. I even went to the extreme of running absurd settings like MAX SOFT on EVERYTHING in the front and MAX STIFF on everything in the rear, and nothing. Even with the center diff set to 90% rear, and as much toe out as I could put in the rear, the car still understeers. Hell, even from a dead stop, full lock to one side, e-brake held and clutch dumped at redline, the car won't even step the rear out! It just plows forward like a fwd car!
So, it would appear that the tuning settings don't, in fact, do ANYTHING! They are just there for show. Now so far, this is the only car that I have modified, so I am not sure if this is just a glitch with this one car, of if this problem is universal for all of the cars, but this is very disappointing. This ruins the whole point of the game, for christ's sake. If this doesn't get fixed ASAP, I'm trading this in and going back to forza. While far from perfect, at least you can properly tune and set up the cars. After 6 years of development and a 70 million dollar budget, this game is very disappointing. Maybe sony should contract turn 10 for their next platform...