I've finally watched it. I thought it was kind of lacking myself, but still had some good parts. As a follow up to Gokaiger, it's kind of odd considering how several things here seem to rewrite the finale. The Gokaiger went to the Zangyack's planet, like in the finale, but for a completely different reason, apparently - The "Most Massive Treasure" in the universe wasn't just a renaming of the Second Greatest Treasure, but even was in a different location. The Gokaiger also seemed to be really sidelined writing-wise, with all the dramatic beats only really hitting the Go-Busters.
For the Go-Busters, their whole plot here seemed kind of, well, forced? From the initial scene with its attempt to show the bonds between the team and the Buddyroids with random expository dialogue to Enter randomly teaming up with the Zangyack without any kind of introduction to that concept. In a way, I guess this felt like the Movie Wars Riders crossovers, with two different plotlines meeting each other. Only here, rather than starting separately and meeting in the ending, they kept touching and then moving apart from each other. It was just... odd to see the Gokaiger and Go-Busters getting individual battles against their own villains and the dramatic beats all hit only a single side of the crossover. Goseiger vs Shinkenger did a much better job of integrating both teams and their villains.
On the other hand, I liked how, just like in Goseiger vs Shinkenger, this felt like a complete story. The villains were seemingly defeated and the heroes won, none of the whole "series villains pop up for a battle but escape, guest team is just fine with it and walks away in the end" issue from earlier Vs movies, like Magi vs Deka.
The action in general was good, but nothing that stood out too much. Mecha battles were nice, but seemed lower budget than what we got in Go-Busters tv itself at times. I did like when GokaiRed and Buster Red broke into the Black Galleon, but the scene afterwards with the Kyoryuger's debut hurt it, considering how the villain had been almost beaten anyway, so KyoryuRed's appearance to help there and their absence from the battle afterwards was pretty noticeable as a tacked on scene to promote next year's team.