It's okay, unfortunately, but don't let that stop you watching! The first 15-20 minutes of this film are great and the animation, vfx and score and even the colour grading were all great. There was menace established in Bowser's character. Some of the sequences were good too, lots of threatening foes and amazing worlds inspired by the games, balanced with a little silliness and humour.
But, then, it starts steaming ahead. And, when I say steaming ahead, I really mean it. The plot moves on very quickly and makes some characters' change of minds or surprise decision-making hard to believe. The moments that we do get feel rushed through and then, as the film progresses, the humour gets younger and younger and unnecessary.
And, don't get me wrong, some silly humour can be okay, and at this point in the film, things weren't too bad. However, there is a moment in the film where Bowser is told that an army is assembled to fight him and they are on their way and Bowser's immediate reaction is to say something like "did peach like what mario did?". This moment in particular solidified some built-up suspicions that the story wasn't taking itself seriously ENOUGH. It decided to take the menace of Bowser and throw a load of childish humour at it, and while that may entertain a child with a short attention span, it took the family element away from this film and started to turn it into a kid's film. But, more than that, it started to turn it into an okay film instead of good.
The film goes right past some key worlds from the game and doesn't do much exploring while the characters are on the journey they're on, which, personally, for me, didn't feel great.
All the characters too, while they had arcs to an extent, they did not have much of a personality or a believability to them which I think is important in a film set in such an outlandish world.
There isn't unfortunately an emotional main story or arc that makes the story feel more profound, so the experience just leaves you feeling that you've watched a breathtakingly beautiful, mindless kids film on two times speed.
But it is not that bad, I think it is an okay film. There were lots of elements I still really like and, some of the world building and environments were engaging and cool. Some of the set pieces were almost there for me in how they mirrored the games. It would've worked for me if there was a strong emotional core to the film or at least a story that takes it's time and maintains menace and threat and has real-feeling stakes.
Overall, if you're interested, go and see it, I hope I've not spoiled things too much for you, sorry this review was so long.
I'm happy to see the box office of this film is helping the industry back on its feet.