It's always really weird seeing a mediocre movie that is getting universally praised, makes you feel crazy. The critics were close to right on this one for once. Also, many of the 5-star reviews are very obviously fake, so be careful with that.
I want to preface this all by saying I'm a huge Mario fan. I've played and own every Mario game and had Mario and Peach cake toppers at my wedding. That did not help my enjoyment of the film at all. I don't expect too much from kid's movies as an adult, but I do expect them to be at least a little entertaining and I don't think that's unreasonable given masterpieces like Toy Story and Megamind. The Mario Movie doesn't seem to be made with adults or children in mind, it's more like it was made for a very select audience of viewers who are stuck 20 years in the past and love outdated humor/slow motion shots.
The story is nothing to write home about, and that's okay, but it is definitely a problem when the story only exists to tell jokes. No matter what is happening, everything will be set aside for a bad joke, or shoehorned 80's track. Speaking of, not a single track that played, even the orchestrated Mario remixes, felt like they belonged in the scenes. It seriously felt like watching a fan-made advertisement for the movie, but the advertisement was as long as the movie itself. As for the jokes, the most prominent was a joke where the scene would go into slow motion, and Mario would say, "Mama Mia." It was inoffensive the first time, but they did the exact same joke at least five more times throughout the movie. Speaking of slow motion, even when it makes absolutely no sense to, the characters go into slow motion. I'd estimate every 5 minutes there was a slow-motion gag (or le epic action scene in slow-motion). The humor doesn't get much better than the mama mia joke, and I would describe it as every single bad cliche from animated movies over the past 20 years thrown into a blender. Everything from characters screaming for no reason, to being lol so rando random, to being cute but excessively dark. The theater I went to was packed, but there were no laughs throughout the entire movie, not even from children.
The animation is really pretty, although that's not too impressive these days. An issue I have with it though is that every action is OVERLY animated. Something as simple as saying a few words will have the characters stretching out in weird ways that make the voice acting no longer fit. On voice acting, most of the characters weren't bad. Except for Donkey Kong. Seth Rogan has no talent as an actor or voice actor, and instead of Donkey Kong feeling like a character in the universe, he was just a Seth Rogan self-insert because, again, Seth Rogan can't act. Stop putting him in movies.
As for some little things, all of the video game references were really forced, aside from the few in the first 10 minutes or so of the movie. This one is totally a nitpick, but they used a lot of stuff from the video game, then totally ignored how it actually works in the video game for a cheap gag or fake suspense. I don't expect it to be 100% like the video game, but surely there would have been better ways to make those jokes.
I don't think the people saying it's amazing are being honest. I can understand enjoying it, but the entire movie is littered with poor writing and humor from a bygone era. Maybe it's not Hollywood that's creatively bankrupt, maybe it's the viewers and their low standards for anything that's "Like the good ol days"