Could be the best PSX game ever.

User Rating: 9.5 | Seiken Densetsu: Legend of Mana (PSOne Books) PS
Of course, this is my personal opinion, but I've always found Legend of Mana to be the greatest PSX game ever made. There's too many people that blindly believe FF7 is God's gift to man, and haven't even played this.

Customize Weapons.
Customize Spells.
Build Golems.
Capture/Train Monsters.

Hours upon hours of things to do while you're not on a quest
(which there are TONS of)

How the world looks is almost completely up to you.
You'll beat it in 10 hours, wait a week, then realize you have the urge to play it again, but the second time it will last 20 hours. Then 30 hours. Pretty soon you won't be worried about beating the game at all. You'll be having too much fun doing all of the extra side options.