I have nothing against green (or any other color of) screen in particular, but CGI PEOPLE are killing a movie. We saw it happening with Jarjar Bings and the weird CGI yoda in episode 1 and the fake appeal of those two character lasted for the next 2 movies, no improvement. At this point I don't think it can be done convincingly. The artificial creatures mostly just look like they were captured with an entirely different sort of camera, and their movements are too exaggerated. The only reason this sort of worked out in Avatar was because basically EVERYTHING was CGI - so a visual harmony was created (entirely fake instead of entirely real). In Star Wars the fake stuff always sort of stood out, in Avatar the real stuff did^^
My problem with CGI elements is that they are never done well enough to feel "really there". Remember how the power suit in Aliens was shiny and looked really heavy? Sigourney Weaver wasn't doing anything, there was a guy maneuvering that thing from the inside, it WAS heavy.
The mechs in Avatar, again, fit in with the rest of the world, only because the rest of the world is fake aswell. Avatar solved some of the "not really there" problems with the help of 3D. When you can put something in a place in relation to the other objects on screen, all the objects become more believable.
So if you do a movie completely in CGI, good CGI at that, and maybe slap some 3D on top you get a good result. But seriously, just about every explosion, crash or stunt I've seen in movies after a certain time (was it 2000? was it earlier even?) has been inferior to the same kinds of scenes when they were done for movies in the 80s and 90s. Light conditions on actors and environments don't match up with each other or aren't sensical in themselves, added camera shakes and stuff also don't help much. When you wanted something spectacular on screen you were required to actually do something spectacular. I'll never forget how they prepared the train accident for that Harrison Ford / Tommy Lee Jones - Good guy has to prove his innocence - movie.
One example for how green screen doesn't hurt movies too much whereas CGI does:
Even the Matrix was still mostly "real", atleast the elements making it up were, they were just composed into events and context that wasn't. Pause the movie when Neo is holding onto the line that Trinity or Morpheus hangs onto after jumping out of the about to explode - chopper. HORRIBLE green screen
But the scene looks way more convincing than a lot of stuff I've seen more recently simply because the friggin chopper was real! Today they would use a fake chopper and the movement of that fake chopper would be just as fake ruining the illusion that a man is being dragged across a roof by a chopper.
Now: Aliens 3. Garbage movie, great potential, nothing to show for it. Significant in another way though. In this one, notably not when James Cameron directed but in this one, they ditched the people in suits aliens for CGI aliens - and the series was dead instantly. They actually went back to (mostly) suits and animatronics in part 4 (also not a necessary watch).