There are plenty of PS1 games that look good and are still very playable.
Pretty much any RPG with pre-rendered backgrounds still looks great (some were water color based!). But as for actual 3D games there are a few that I find very playable still, however thanks to emulators, they look even better with higher z-buffering and interpolation:
Ace Combat 3: Electrosphere - Still my favorite AC game, and easily the most original and boldest. It's a shame the NA and EU versions were chopped up as opposed to the JP version.
Silent Bomber: A rare little gem from the PS1's final days that not only looks good but is an incredibly well built game-aside from the English dubbing. The explosions are still fucking AWESOME.
Crash Bandicoot games: Before Naughty Dog left Universal and had to leave this series in the hands of Universal out of contract agreements, it was still an amazing and fun series that really helped to define the PS1.
Spyro: Just like Naughty Dog, Insomniac had to leave this series with universal out of contract and of course the quality went down the shitter. But it's still fun to take a trip down memory lane. The original is my favorite platformer from the entire 1st Generation 3D era.
Now when it comes to the Final Fantasy games (in particular 8) I think people really don't give alot of credit or actually forget about how freaking awesome the GF summon scenes were. They were amazingly well built, and sometimes I can't believe the PS1 could even render them when I go back and play. The one that always comes to mind is Ifrit's summon and attack. That coupled with the extreme vibrations of the controller and me desperately trying to boost his attack power with SELECT + Square button was just awe inspiring.