I think another reason CGI often seems obvious is that it always looks too perfect, too shiny. Movie makers try hard to avoid this, but it doesn't work very often. I believe the reason the CGI in LOTR worked so well is that the characters weren't "uniform", ie their left side lookeddifferent from the right; whereas the clones on AOTC were very uniform, and the shiny uniforms look more plastic than the textures on the orcs etc in LOTR. Plus all the clones looked exactly the same (obviously) which again looks unnatural. Even the stormtroopers in the OT look slightly different; they all wear the same uniform, but are slightly different heights, have slightly different stances, have slightly different amounts of black and white showing etc, and the eye picks up on these minute differences, which don't exist in AOTC.