I am an animation junkie, a Disney stan and I will watch basically anything with a magic princess in it. So I probably am not the most unbiased person in the world but I really liked it. It had a couple issues but overall it was pretty darn good, also it's a really beautiful movie, the visuals alone really sold me on it. Plus you pretty much don't even notice the Rock unless you are paying a lot of attention to it.
Also to keep this on topic, Baywatch was a complete and utter mess of a show that was fun to watch because it was incredibly stupid. The movie seems to keep on that trend so it's no wonder why critics hate it. It was never going to be a movie for them and if it was it just wouldn't be baywatch. Like at one point Baywatch was one of the biggest shows in the world ... but I don't think it was even ever nominated for an emmy or anything. It is what it is, a dumb comedy with a nonsensical plot. If you're into that go see it, if not then steer clear.