I haven't actually played much variety on the PS1 at all, so my list reflects what I've played and had fun with. I won't for a moment claim that there aren't a lot of much better games.
1. FFVII
2. Bushido Blade
3. SOTN
4. Parappa the Rappa
5. Tenchu: Stealth Assassins
6. D
7. Star Wars Masters of Teras Kasi