I've been mostly disappointed with PS One classics. Like some users said before, they're too old. Most annoying thing aren't even the graphics, but the gameplay mechanics.
Jump'n'Runs were mostly satisfying though.
I'd recommend you Crash 2 or 3 (the first one isn't as good) or both Abe's Odyssey and Abe's Exoddus. Crash Team Racing and Kula World were good too.
I've also played MGS, Syphon Filter, Medievil, Driver, Rayman, Soul Reaver, Final Fantasy VIII, and a lot of big names from then (mostly as PSN Plus gift), and was disappointed of all of them.