The GT90 isn't a perfect car, but with a little tuning, it can be a lot of fun! Recall that there aren't too many 700+hp mid-engined cars that are grossly overweight, so treat the GT90 like you would the Speed 12, for example. It really doesn't require much tuning...don't give up on this car (because it sure is difficult to get back)!
It lacks a 6th gear, which is my pet peeve with the car. You'd figure a concept car might have that sort of thing...