Every bad thing you've read about it is correct, but it doesn't add up to as horrible a movie as some of the reviewers suggest. It's just insipid - that is, Cats - with bad jokes and badly conceived cat-human hybrids.
I don't know if Rebel Wilson chose to or was forced at gunpoint to reprise her character from Pitch Perfect, but the jokes they wrote for her, or that she ad-libbed, were at the level of "look what the cat dragged in" (yes, that's a real example). Another attempt at humour, which to her good fortune she did not have to participate in, was a cat smashing its balls jumping into a trash can.
While there are some outstanding performances, neither the female lead nor what kinda-sorta seemed to be a male lead was among them. The female lead, to be fair, is a ballerina, not an actor. Her dancing was great - all the dancing was great, and if they'd looked more human it would have been less unnerving and more purely enjoyable - but her character's facial expressions were limited to naive excitement at everything (and maybe that's all they wanted from her). It was weird, though, because she wasn't the country cat who's excited to be in the city, but a cat who is literally thrown away in a bag in the first scene, so a little more emotional trauma would have been in order.
The male lead exuded great sincerity and an obscure sense of self-importance while being quite stiff and wooden. And yet he was not Keanu Reeves, only a more irritating knock-off.
But it's the CGI that makes the movie bad. First, I hate all CGI or other special effects used to violate the laws of physics (unless the character has a special laws-of-physics-violating talent). Seeing cats sort of float when they jump just doesn't work. And I have no idea what the supposed break-through with the digitised fur is. I remember seeing the waving fur in Monsters Inc., and being blown away. It was cool. I noticed nothing here, and I looked. Whatever this breakthrough is, I guess it's very subtle. And it certainly doesn't overcome the disturbing cat-human hybrid conceptualisation of the critters. Why are there faces so human, but with whiskers (only sometimes noticeable, though), and some seeming to have fur all over their faces and others with fleshy cheeks? Why do they have human hands for heaven's sake?
But all that adds up to is a bad presentation of well-known story. It's not the horror-show of the century, just something to set back the career of a few people for some time.