Final Fantasy III is indeed underrated, it's original NES version is as loaf said plain awesome. I always thought IX was underrated until I saw just how huge fan base it has, including the developers, and how well it was received by critics. I wouldn't exactly say XII is underrated, though it suffers from "either you love it or hate it" deal. As for the other side of the coin, Final Fantasy IV and VII are in my opinion highly overrated games.