Both the Suikoden and Breath of Fire series' have managed to maintain decent track records for sequels, despite having some flaws here and there. The Wild ARMs series is also rather pleasant and has an interesting history behind the games, I enjoyed the change from a fantasy setting to a western-based one.

I believe the second SaGa Frontier game outshines the first by a longshot, or it could be the other way around, I'm not sure as I haven't completed either. Just heard some things.