Wheelbase and stance errors always bug me, and of course what the American companies do with wheels and tires, although there are some notable exceptions. Blunders on the body dimensions are a big problem, but they can be corrected, usually. The way some grille/headlight/bumper areas are addressed has turned me off on a number of kits. I can fix a lot of stuff, and swap wheels and tires, but the work required to alter the front end and then send things out for plating if needed is just ridiculous. Some of the kits have only a passing resemblance to the real thing.