The ones that take place during the show are pretty good. Heisei Generations Final happens fairly early though, so there are some oddities with Banjo's characterization, and it's also a crossover with Ex-Aid, OOO, Fourze and Gaim, heavily spoiling the endings of Ex-Aid, OOO and Gaim. The solo Build movie is pretty much a conclusion for the daddy issues arc, and that part it does well, although the villains themselves are oddly downplayed
they're hyped up as other members of Evolt's race, but then it's revealed none of them have drivers and so they need an insanely convoluted plan just for one of them to get close to Evolt's level, while two others are stuck as Smashs. The whole plot would have worked much better if they all were Riders. They could just have reused Evolt's suit and gave it new helmets for each one).
The post-series movies are more controversial. I wasn't fond of the Cross-Z one and what it does with Build's ending (Heisei Generations Forever, which is more of a Zi-O movie featuring Build's characters feels like a better follow up to Build's finale), but the Grease one (which actually heavily features the entire cast) was a good conclusion coming from Cross-Z's set up.
