Star Ocean The Second Story is a great game. I've finished it at least 7 times or something (yes, I have no life sometimes :P), beaten the bonus dungeon multiple times and even finished the game on Universe mode (for ppl who hasn't played SOTSS, there's 3 difficulty levels, the 2 harder ones aren't available at first though.. and the toughest one, Universe, provides a tremendous challenge).
It's simply a great game. The battle system is awesome. I've never enjoyed battles as much as I did in SOTSS. The item creation system, the bonus dungeon, the 3 difficulty levels and the 80+ different endings (based on how you treat your companions) gives this game an incredible depth. Not to mention that there's also 2 extremely difficult super bosses (even on the easiest difficulty setting they are extremely difficult).
I've been eager to play SOTTEOT as well, but I haven't been able to yet. I will in not too long though
I've also played the original SO game for SNES (it was never translated, so you need to run it on an emulator with a translation patch, plus, the game uses some special type of encoding that it wasn't even playable on emulators until pretty recently). It's a really good game