Suikoden 2, easily; you should've heard my hype when I discovered what transferring Suikoden 1 data gave me. Although, frankly, it's been long enough that there's a lot that I don't recall. Same for other stuff I'd say, like Xenogears, and other stuff, like FF6, I played so much that I've memorized the secret stuff, forgotten they were secrets, and now treat that stuff like it's the main path through the game, so I'm not sure I can even forget Chrono Trigger and FF6/7/8 anymore.
Maybe Final Fantasy: Tactics. I'd love to play through that blind again, especially with the remake on PSP.
Maybe fighting games in general? After playing them long enough, you start to learn habits for finding combos and strategies and stuff. I'd like to rediscover all that.
Breath of Fire 3/4 are good contenders, too. Which reminds me that I should play Dragon Quarter some time.