One of the games I played back on PS1 was Dino Crisis 2. It's a survival game where you got stuck age of Dinosaurs. The story is a bit complex and hard to explain (but is good nevertheless.) The gameplay of this game however is very good.
Like Resident Evil games of that time. Dino Crisis has 3D characters on pre-rendered backgrounds with fixed camera angles.
But what's amazing about this game is its sound. I'm not talking about music (which is also good) but the sound effects. The game uses a fixed camera to hide some dinosaurs from the view. While that might increase their difficulty, this is offset by the sounds the dinosaurs make.
The sound of their movements, their footsteps as they break through the bushes. The clanking sounds as they stump through a factory. The heavy weight of their jump. Their quiet hissing as they approach their prey. Their grunts of pain as your bullets penetrate their scales.
For a PS1 game I was always amazed by how the sounds make help the player in this game. Dino Crisis 2 is one of the games that uses sounds effects right in late 90s.
I can't play this game if its audio isn't clear.