Of course, the answer depends totally on which particular model(s) you're talking about. Some parts are done very well on one model, terribly on another.
As far as how many models are affected, I'd say unrealistically flat interior panels. Most cars, especially those older than the 80s, had window cranks, interior door handles, door lock pins, etc. that stood out from the surface. How many times have you seen a model with the interior panel details just sort of hinted at... or ignored altogether. It's especially obvious on convertibles, where the interior is the first thing you notice.