Grandia 1 & 2(Haven't played 3) - One of my favourite turn based J-RPG battle systems, I always thought the earlier Final Fantasy games could of took a couple of lessons from this game.
Shadow Hearts Series - One of the best J-RPG's ever made. It has one of the most creative and additive combat system made. The story is dark and funny at the same time in a very good way. A MUST play for any J-RPG fans. Actually I only played number 2, but if the others are half as good I'll be pleased.
Final Fantasy 5 - Most Final Fantasy games below 7 get over looked a lot and rightfully so, but this was Perhaps the most underrated of all Final Fantasies, typical Final Fantasy game play, but good storyline, likeable characters, and the job system was really good and one of the main reasons its on my list. If you have to play a FF game below the release of 7, play Final Fantasy 5.
Breath of Fire 5 - The thing about this game is it is the only RPG I know of where your character's life has a timer throughout the whole game. Alot of replay value, it has this formula where you get to replay the game, once he dies, while still progressing, I guess you have to play it to know how good it is. People have said Breath of Fire 3 was underrated, but I've only played number 5. A very unique formula that I've never really seen duplicated in any other RPG.
Second sight - Great storyline, even better plot twist at the end of the game, and great uses of stealth, mind powers, and guns for your shoot em up kicks.
Shadow Hearts is a top-tier game and Yuri Hyuga is a top-tier hero. I haven't played number 2, but number one is great (never completed it though ). It had an amazing setting, atmopshere and soundtrack.
Grandia xtreme was technically a spin off, but it's my favorite out of all of the grandia games, much better then Grandia 3 in my opinion.
lol i thought i was the only person to ever play that game, it was pretty darn good.
Overrated: GTA and FF
underrated: DIRT and the splintercells