Walking carpet, timdiggerm, good points.
I just stepped through AOTC looking at effects shots; here's what I noticed.
-Actors are often composited directly into model or CGI environments. In the OT, mattes were used to extend sets (docking bay 327 on Cloud City, the Executor bridge, etc), but the actors were on a mostly real set with real lighting. Not only does this automatically look more natural, I think it allows for better shot compositions, because you can take advantage of the geometry of the set, the lighting effects, etc... instead of everything being a two-shot against some to-be-determined background that may or may not really work against the actors' placement in the shot.
-Things move strangely. Aliens are sometimes very animated, and missiles, energy trails, explosion debris, etc, all follow twisty paths through space, which might be cool a few times, but it happens a lot.
-On a related note, the lighting from said explosions/projectiles seems off, probably because it doesn't bleach out the shot the way a real huge explosion would. Rich orange tongues of flame sometimes seem out of place (the destruction of the flying wing at the beginning of AOTC sticks out in my mind).
Relatedly, the lighting on CG objects often seems flatter (or less stark?) than normal, which exacerbates the amount of visible detail (sometimes so much that it makes things look unrealistic, with tons of circuits and things all over) as well as making the objects in question not look like real objects.
Compare (apologies for the image heaviness, but I think it's illustrative):
