People's relationship with CGI is always negative, whatever the quality. To say that the CGI is average would be to say that the anime is rather average in its animation, and that would be a lie. The CGI in Girls Band Cry isn't "average", it's objectively good. The dinamism is there, the scenery works well with 3D, the characters don't lack facial expression. In general, we tend to accept bad 2D rather than good CGI.
Bad CGI is often recognizable with a lack of expression and jerky animation. I don't think "Girls Band Cry" can be considered average CGI.
The episode was really surprising, and the staging and choreography of the opening looked very polished. I can't wait to see it!

CGI anime has come incredibly far, i've been a fan of Houseki no Kuni and always give 3D anime a shot, and this show has incredible and lively animation especially for such a "casual" slice of life genre, hopefully we get more studios adapting in 3D and more viewers accepting 3D animation, cause it can pull off so many things which just wouldn't work with 2D animation, raaaagh
Unless you're GoHands, people typically complain about CGI when it's blended into 2D art. I've personally never had an issue with full CGI anime like Land of the Lustrous, Hi Score Girl, Knights of Sidonia, etc.