Oh Chrono Cross, what a dirty little secret you are. Seems like everyone who wants a sequel to Chrono Trigger never played you.
My last regret is probably Mario and Luigi: Partners in Time. The story just annoyed me and the gameplay could have been so much better with a little more depth. The Harvest Moon for the GC was a mistake as well. I would say I regret buying Super Paper Mario, but someone gave me it as a gift because they figured I would love it (and so did I). I don't know what they did wrong with the game to make me hate it.