@PG1315 I've played a little of every Minigame now and imo it's really fun, just a little restricting.
There are four movies to choose from (being Godzilla 1954, TroG, Shin Godzilla and GvK) which each offer a different kind of mission. It varies from fighting other Kaiju to building defenses, the only thing that I find a shame is that there's only one kind of Minigame per movie.
I'm sure it would've been cool to survive against Shin Godzilla or fight as a MonsterVerse Titan. Apart from that, collecting missions allows you to win statues and posters of the monsters from a slot machine, with them being displayed in four different rooms ordered by era.
All in all I can tell that a lot of effort was put into it, and I do find it very fun. It simply could have been a little better.