Out of all the RPGs I've ever played, I can easily say that SMRPG had the highest replay-value. In fact, me and a friend recently started doing a "low-level, first available equipment only and only the special attack/special def-choice during level-up" challenge together. We are currently at the sunken pirate ship.

Toughest battle so far was Croco 2 (Croco in the mines). But it wasn't too bad still. Things will probably get a whole lot worse later on though.