CGI just isn't believable. I can't quite explain it. I don't know if it's that the director is trying too hard or something, but something just fails to resonate properly.
Consider "The Dark Knight" -- from what I can tell, there was very little CGI used in that (apart from that sequence at the end with the cell phones). That movie looked remarkable, and really kept you "within" the movie.
Then consider something like "Indiana Jones and the Crystal Skull" -- apart from being a terrible story, it just LOOKED terrible. Cartoonish even. I just found myself overly conscious of digital animation going across the screen. It just looks tacky.
Honestly, I would prefer the low-grade "special effects" of something like The Exorcist than I would most CGI these days. There's just something about it that makes everything really dull.