Yokai Watch is, in a nutshell, a Pokemon imitator that actually tries a few new things, which is why it stands out from the crowd of Pokemon imitators and has become such a success in Japan. Of course, much like Pokemon, they had to have their opportunity to show off their success on the big screen!
That success has partially translated over to the international side, however not to the same extent as Japan. That's probably why this movie was only in theaters for a single day in America, and wound up quickly popping up on television and Netflix.
It's clear from the beginning of this movie
that it doesn't take itself too seriously and recognizes that a lot of its audience will consist of ADHD children. The first two minutes are devoted to a sketch of familiar characters (to anyone who's watched Yokai Watch, at least) trying to tell you to enjoy the movie but winding up in some silly slapstick situation.
The story itself isn't a fresh idea, but it's one that's easy to tell/put a new spin on and easily captivate a child audience, involving time travel and a child going back in time and meeting their grandfather as a kid. The presentation is pretty entertaining, thanks in part to Nate's sidekicks Whisper and Jibanyan, who are very much the comic relief of the story.
As usual, Yokai Watch has a cruder sense of humor than Pokemon, so expect some fart jokes and a joke about pulling a cork out of a yokai's butt. Though it seems like they avoided some of the more devious innuendo from the TV series this time, perhaps recognizing that more parents would be in the audience than usual.
Towards the end of the film, there's an extended sequence in which pretty much every yokai from the series pops up. There's a purpose to this in the story, but there's also another purpose the producers were certainly thinking of: showing off cool yokai for kids to get excited and point out to their parents. That's when it hit me: for some kids, this is going to be their "Pokemon: The First Movie". They're going to have it on loop on Netflix and be obsessed with it, while their parents are just kind of lost/long for the days of PBS, but don't say anything because they recognize the movie as largely harmless.
If you're a fan of Yokai Watch, you won't be disappointed by this movie. It's nothing outstanding, but it's a good time with familiar characters. If you aren't a fan of Yokai Watch, this won't convert you. If you know a kid who's a fan of Yokai Watch, showing them this movie (if they somehow haven't seen it already) will likely delight them and make you happy that they're happy.