First of all, I always thought that a special effect is done correctly ONLY if you don't realise you have just seen a special effect !
The original Yoda puppet used for Episode V and VI was an example of a correctly done "special effect" - even now, when I have seen literally hundreds of movies, most of them special effect-oriented, and I know how Yoda was created, when I look at the 2 movies, he looks REAL to me. He really looks like a little grey-green old alien warrior-philosopher. He simply looks REAL, and he delivers a great performance. BTW for many years I thought he wasn't a puppet, I thought he was simply a midget in a costume, that's how real he looked (and looks) to me!
However something very, very bad has happened in the prequels. The TPM puppet looks like - well, it looks like a puppet. It looks nothing real, it looks like a poorly done puppet. The magic from the original trilogy didn't happen. So what did the ILM fools do ? They replaced a crappy looking puppet with a crappy looking CGI model. The puppet looks like a puppet, and this new digital Yoda looks like a cartoon character, I can't decide what is worse, but one thing is for sure - I hate Yoda in the prequels. They have done absolutely EVERYTHING wrong - the level of detail, the movement, the ears, the face ... everything looks good enough for a cartoon, or a video game, not for a movie