The movie does have significant weaknesses, as the other comments point out, but there are a few strengths worthy of note.
I was positively impressed by the global level of detail of scene backgrounds. Where in other CGI movies you get to see, say, a row of buildings with carefully modelled details near the camera, then a lot of empty space behind those, and finally a matte painting of the 'horizon', Back to Gaya shows you whole blocks of buildings, with the next streets showing through the gaps, all in credibly full detail, but without any obvious repetition of similar structures. To me these shots had a sense of realism that I had not seen before in CGI movies.
Along the same vein, when there are open air views, the distant landscape is never a simple background painting, but a detailed model. As far as I can tell, even the clouds in the sky were actual 3D entities instead of the usual flat background painting. This gives the camera a lot more freedom to move large distances and freely look around the scenery. The filmmakers probably overused this freedom somewhat, though, making some scenes hard to follow.
The outstanding level of detail extends to things like vegetation interacting with buildings, like plants growing inbetween and around fenceposts, for example. What I also liked was the general worn and aged look of things, a refreshing change from the polished featureless surfaces that are all too common on CGI movies' background objects.
The character animation in comparison is two classes below that, as the other comments mention. One thing I like about the characters, though, is the courage of the designers to go for the outright bizarre with the 'human' roles. It was interesting to see character design exploring a different direction than the usual either hyperrealistic or more classical comic style.
So, despite its weaknesses, Back to Gaya actually manages to advance the state of the CGI art on a few fronts. I do hope that it will be commercially successful enough that the makers get another chance to apply their talents to a better story.