Went to see it yesterday.
And for once I agree with the lowish score of the critics.
Yes the movie was great fan service but that was the problem as well.
It was crammed so full of Easter eggs that they kinda forgot the story and just jumped from scene to scene at ADHD speed... on speed.
Whole movie felt like the director just read summaries of all Mario and Luigi related games and crammed them in there and then peppered loose stuff as additional Easter eggs. And then tried to point out the Easter eggs.
I was very disappointed.
Yes you should watch it but I'd say avoid until you can see it for free and have absolutely nothing else to do.