I see a lot of people defending the criticism of it just not being what people expected, but I haven't actually personally seen many criticize it for that at all.
The problem for me was more with how they told that story rather than the story they chose, and a lot of the details just not being consistent with what is established, and not capitalizing on what TFA set up, but instead undoing it. And the humour was added to the film in a way that wasn't natural, and hurt so many important moments that should have been serious. It took me out of the film. When a film makes me groan out loud within the first ten minutes, it's a bad sign.
I think the overall plot was just fine, and there were a lot of good scenes, but I don't think they knew how to tell this story most effectively and got some details very wrong for the bigger picture imo. Maybe it was too many cooks in the kitchen trying to appeal to the mass audience, or maybe it didn't quite fit Rian Johnson. TFA and Rogue One were both very enjoyable films for me, but this movie makes me concerned for the franchise going forward, and I'm not even a SW fanatic.