For me it's Chrono Trigger. I always want to play it. I want to show it to my children. I hope it will be regarded as a masterpiece for generations to come.
The Jak and Daxter series. Gameplay still holds up, story and world building still holds up, and it's been made easily available to later generations of consoles. Heck even the in-game animations hold up shockingly well, Jak's movement feels so fluid and organic compared to a lot of other older games that tend to feel a bit janky compared to modern games.
Older games in the Ratchet and Clank series also hold up pretty well too, though they're a bit harder to access unless they've been made available on the ps4/ps5 since I last played them, otherwise I have to dig out my ps3 to play the first 3 games.
I replay both game series pretty regularly and they're always equally as fun to play no matter how many years have passed.
if you aren't aware, the ps3 you can dig out from the internet works really well and lets you get higher rest and a more fluid experience, even on a pc that isn't top of the line
The PS3 emulator, RPCS3, runs most of the entire Ratchet and Clank series very well. The only ones I really had issues with were A Crack in Time (it's just not as optimized) and Into the Nexus (again, not too optimized, but more so. Had some frame rate issues). RPCS3 is only getting better and better!
I have to say I haven't tried many games on it, which I probably should since the ps3 was at the time known for it's exclusives, but I did devour Wipeout HD fury on it ad it was incredibly smooth
I've played quite a few games and have only had major issues with a couple. A lot of times there is a patch available in some way for issues, or a setting to change, but these are almost always listed on the RPCS3 wiki so it makes it super simple. Of all of the emulators that I have used over the years, this one is by far my favorite!
Definitely check out OpenGOAL. It is the best version to play right now (even better than the remasters for PS3/4). It is basically a native port for Windows and Linux.