I think overall if I had to lean one way or the other it's that I enjoyed it. It's always going to be pretty impressive to me when a movie can tell a cohesive, solid story (even if it is fairly simple) with no dialogue. The animation itself was pretty impressive for a multitude of reasons. The camera movement in the movie actually looks pretty real and natural, like it was filmed with an actual camera as opposed to what you often see in animated films where it's just kinda following the characters flawlessly and looking at what's going on. The movie in general really just looks really good, and in particular the water itself is done pretty well. I'd even go so far as to say it's the first time in a long time I thought a movie came close to holding up to Antz in that regard, which is my gold standard for animated water. Everything about how the movie looks and is animated is also particularly impressive knowing that the movie was made in blendr, though admittedly there are a lot of times where you can kinda tell, especially anytime our kitty protagonist carries and drops something. The animations of the animals in the film themselves are also surprisingly well done. If everything didn't look so stylized, like if this was Disney "live-action" Lion King quality visually, but the animations were largely kept from Flow, the animals would just look real.
It's a little bit of a hard watch, though, if you don't like seeing bad things happen to animals, even animated ones. The fact that they feel so realistic despite being obviously animated makes when any animal character is in distress hit a bit harder too. I think the only outright problem I had with the movie is that there's a couple plot points (mostly involving a group of dogs) that just kinda feel completely unnecessary. Like, if they were removed from the film, it just wouldn't be different. The movie also starts leaning pretty heavily into being a bit more symbolic and mystical towards the end, but that also kinda makes it feel a little more incomplete too. I should also add that for me, it feels longer than it is. I thought the movie was around about 2 hours, but it's a little short of an hour and a half. That's not to say it's poorly paced or anything, because I wouldn't say it is, but there's a lot of things that happen, and the movie is fairly regularly tense because it's a mishmash of confused animals trying to survive a great flood on a boat for about an hour and doing about as well as you could reasonably expect.
I think if I had to sum it up shortly is that Flow is a mildly distressing movie about animals trying to survive by not drowning,but it's really pretty and is overall a pretty solid movie. Would recommend, but maybe not to everyone.