Nostalgia obviously plays a big role, but to me what was awesome in 90s gaming (well, for me personally: late 80s up to early 2000s), is how you could really see the technology advance: from CGA to EGA to VGA (and then the full videos in Command & Conquer!), from bleeps to soundblaster and full midi support (I heard voices for the full time on Dune 2), and the new forms of gameplay, better AI, better level building (2D maps in Wolfenstein, pseudo-3D in Duke Nukem, full 3D in Quake), and so and so on.
I don't know if that's still true for today's gaming experience: I largely stopped for about 15 years and have no idea what's top of the line now or special now. But it was definitely really cool in 90s gaming.
But yes, there are definitely also a ton of games I remember fondly that weren't special at all in terms of technology, and that I'd probably rather not try again, not to ruin the memory.