I liked how it was open-ended, and to be honest I don't regard Advent Children as a sequel, more of a fanfic movie actually made by Square Enix. My only issues were the pointlessness of the battle which you don't actually fight in, and that there was no alternate ending with Vincent and Yuffie in it, but I did enjoy the ending sequence. I liked how you were left unsure if the world was saved and evrybody survived (except for the after-credit hint).

It would have been nice if Sephiroth was harder, but I guess he is easier to satisfy both the speed-gamer and the completionist.