It's not even a disappointing sequel, if you go into it with the right expectations. That is, "a game that builds upon the themes and ideas laid forth by its predecessors while retaining a similar atmosphere and feel". Which is what I want out of a sequel, especially in a video game.
If you want a sequel in the sense of "another fantasy game with time travel", go check out Radiant Historia. That looks great, and as close to Chrono Trigger 2 as there ever will be.