Other : Reinsert the experience system, so farewell Star levels.
I really like Cross battle system so I would not change anything about it.
Of course, more background for the characters who are not called Serge, Kid, Lynx or Harle would be wonderful.
One thing I can't tell if I'd change it for Chrono Cross or another Chrono game is about the main character. I don't know if that "silent protagonist tradition" is a good thing or not.