For a Diend fan, this is really a pretty solid outing, giving him a chance to exhibit all his trademarks. He uses some of his usual tricks, although probably better than ever before. He of course gets one particular new one that you probably already know about. Needless to say I liked it. Its introduction is a bit odd, but if you're used to how some past Heisei Riders got their new toys, it's pretty much in-line with what we've come to expect. You'll like that final attack, no doubt.
The movie's other main star is an interesting character, or maybe I should say characters? There's a pretty good storyline going on with him and you might be surprised at who the actual villain turns out to be. It's signposted, but the way the movie went about it was interesting and not what I expected.
The new Rider, G Den-O, is okay. As a costume it's pretty much what we've come to expect from movie Riders in Den-O, that being they took the basic Den-O Plat Form look and changed around the armor here and there, new helmet there, etc.
As for the rest of the cast: at this point I've just run out of things to say about the regulars. We had them in the last two movies, we've had them before that, etc. Mizoguchi is still amazing, Momotaros is still hilarious, with one scene that's become one of my favorites ever involving the character. And everybody else is about what you'd expect.