It’s a common complaint among the anime community is that 3D CGI is general terrible. I’m not going to say that there’s nothing good about CGI but I haven’t seen any I liked. The newest Berserk is primarily CGI, I found the character models to be very stiff. I think full 3D is worst than the blend of 2D and CGI.
Fate/Zero does this very well. CGI is best when it blends in so well that you don’t notice it. I think that is actually an indictment of CGI. Fully 3D anime can be “cut frames” poorly. Finally, CGI just doesn’t flow as well as 2D. To be clear 3D CGI can work, but it seems to require a healthy bit of 2D. For more insight on why CGI can be bad you can read this article. If you want to see an interesting video on how they blend 2D/3D check out this video.