when you can tell it is CGI, it can take away from the movie; however, I have low expectations when it comes to movies and can let a lot slide.
E.g., in Spider-man I, the radioactive spider rearing up to bite Peter Parker was a ruining moment for my wife. When Peter is jumping from roof top to roof top was obvious CGI. i let it slide, but that i noticed and had to make that adjustment was an effort i would have preferred not to have made.
on the other hand, the Thing in Fantastic Four might have been a candidate for more CGI vs. the suit. according to Marvel Universe (from the 80's), they explained why The Thing looks the way he does now (or at the time) from when he was first introduced; that given the altered DNA, his body evolved over time. if the right mook does the research, this could be addressed by adding CGI details to the suit worn by the actor (whose name is escaping me, and i want to refer to him as Vic Mackey/The Commish), so that he looks more like living rock and less like a guy in a suit.
Your Friendly Neighborhood Creepy Old Guy