These are games I still sit down to replay to this day, mostly on emulators
NES: Super Mario Bros 3 - only playable on emulator because it has archaic limited 1 ups that give you game over
SNES: SMW which is not as cruel, so can be played on actual hardware, along with Super Metroid, Yoshi's Island, and DK lC 1, 2 and 3 (I think I'm the only freak who prefers 3) (DKC is also too cruel without save-states for me to consider playable)
On Mega Drive: Rinstar and Gunstar Heroes. (again, I can't endure Gunstar without savestates)
N64: SM64, Mario Kart 64 and Rayman 2.
PS1: Crash and Spyro 1, 2 and 3 (now I can play the remasters, but somehow I still like to play the originals to appreciate the impressive graphical feat they pulled off in those games back then)
and what I think is the best Kat Racer ever made: Crash Team Racing. Also, klonoa.
Old PC: Most of the comedic LA graphical adventures: MI1, 2 and 3, DoTT, S&M:HtR, FT. The ones before MI1, Loom and Dig are a bore.
Half Life 1 & 2.
That's it. The list has been longer, but the avarage game quality has risen too much for most older stuff to still hold my interest.
There are few GC/PS2 era games I'd still play today, but I'm still eagerly waiting for the day all kinks in their emulation are sorted so I can safely do it:
GC: SMS and Mario Strikers.
PS2: Jak Series, but J&D1 is the best in my opinion, the GTAzation of the later titles, beside being cringy added all the busy work of GTA with none of it's thematic appeal nor emergent fun, while also diluting what made Jak 1 good.
I would also give Ratchet and Sly games a try, but I didn't find them as enjoyable back them and I'm pretty sure it would be worse today.
XBO: Splinter Cell 1, 2 and 3.