My opinion is that you're wrong. The CGI was amazing in this film. It looked like an actual Godzilla stomping around, battling other monsters, breathing fire, etc. After a lifetime of seeing so-bad-it's-good schlocky unintentionally comedic Godzilla films with a guy in a foam rubber suit stomping on fake cities made from balsa wood, it was a breath of fresh air to see a properly made Godzilla film. That's not an insult to the older films. They are fun, and as a child I loved them, but this is the only Godzilla film that an adult can watch and re-watch and enjoy as a proper film.
What exactly were you looking for in this movie? What about the CGI looked even remotely bad to you?
Godzilla the creature was ok, for an animal that doesnt exist. However, contrast it with the dinos in jurassic park, whose exact appearance nobody knows for sure. Those animals looked complelely believable, like they were actually alive, but they were combined with shots of animatronics to sell the reality. The cgi in Godzilla was clearly animated and unconvincing. The human brain is very adept at telling when something looks fake which is why cgi rarely looks entirely real when rendering living things.
Overall i found the effects work to be videogamey in godzilla, a trend that seems to continue today when you would expect more progress to have been made.
Nothing in Godzilla looked remotely fake to me. It looked as good as anything in the new Jurassic Park film, and much better than what was in the originals, which makes sense given the passage of time. This must be a case of two people seeing two different things, though I wonder if anyone else found Godzilla to be unconvincing.