Endings can be a very fickle thing for people to deal with. If a series you loved ends badly, it can reverberate all the way to beginning, bringing into question wether you even really liked the series to begin with. Such is the tight rope act Kamen Rider Decade has had to endure. With 31 episodes of build up to a promised cataclysmic ending - the finale Decade story simply had to be good. If not, then what was the point? Well, as this movie aptly puts it, it's the journey that's important.
This movie features two completely separate storylines, featuring the ending battle with Decade, and the beginning origins of Kamen Rider W. It's all very parallel to each other - finally ending with a shared crossover, where Kamen Rider W is suddenly shoved into Decade's world. They both fight together and defeat their foes. It makes absolutely no sense -- but, that's what the Japanese really are good at: taking a situation that, logically shouldn't work, ignoring that logic, and making it work anyway. There's no reason why W's story had to cross over into Decade's story. At least it made some kind of weird sense on Decade's end, who deals with multiple dimensions. But it still worked.
There was no revelation of Decade's origins (I suppose the All Riders movie is cannon, now). And there where such strange homages and events that even long time fans might not understand. (Why, exactly, is the grandfather turning into an older-style Rider villain?) It might not be the ending everyone was expecting - but, it's and ending. And I, for one, am completely satisfied! They threw in everything for this final battle - even a robotic elephant! It was just awesome! And, as for Decade, he's still going to be out there. Maybe we'll see him again if we ever need another Kamen Rider series cross-over. In the meantime, he'll continue the journey. Whatever you thought of the ending, it was quite a journey - and nothing should take away from that.