The simplest explanation that I can give you is that, CGI is 3D and more often than not it is very awful 3D and normal animation is just normal 2D animation.Can ANYONE explain what's the difference in CGI and the normal animation. Isn't that "Computer Generated Imagery" too? I haven't watched even a single episode of Ajin yet so I don't know. But hey, that won't even bother me a bit, all I care about is the Plot. XD