Generally, any top rated game from that period which doesn't rely on "realistic" graphics but instead offers very good gameplay and is kind of timeless and ages well. For example, you shouldn't play the original System Shock 1 anymore, although it was top tier in 1994, because its graphics are very poor for today's standards, it's UI has always been poor, and it's a game that fully relies on immersion, but you can't immerse yourself anymore if both graphics and UI are really poor. Instead, play the System Shock remake from Nightdive Studios which came out recently. It's not the same, but it's very similar, and much better nowadays. Also why you shouldn't play the old STALKERs anymore, although they were amazing and it kind of saddens me to write this, but they really don't offer much immersion today, which is why they didn't age well. I'm writing this because I didn't finish part 3 back in the day and intended to finish it like 2 years ago, but I couldn't stand the dated graphics anymore. For a game which relies fully on immersion, that ruins it.

Here's my list (not in a particular order), I'm focusing on PC games because I never really play that much console or handheld stuff:

• Command and Conquer up until Red Alert (remastered version available). These are classic RTS games in a sci-fi war setting. Some say Total Annihilation was the best RTS during the 90s but I never played it.

• Starcraft 1 (remastered version available). This game is also still being played competitively in multiplayer, with an active tournament scene, especially in South Korea. Also great in single player. Famous for its balance, at least on modern tournament maps.

• Age of Empires 2 (remastered version available). It's like a mix between a classic RTS and Civilization. Great game, lots of content by itself already, also tons of added content.

• Jagged Alliance 2 (great community mods available). You can skip part 1, part 2 was absolutely amazing. A great strategy and tactics based game. It's quite difficult, but great.

• Doom 1+2 (remastered version available, very recently updated again on Steam (this month!)). Plenty of 3rd party engines like gzdoom also available which make them look and feel much more modern. Tons of community-made content as well. Special mention: John Romero, one of the original level designers, also made more content over the years (e.g. "Sigil"), which is great as well.

• Quake 1+2 (remastered version and 3rd party engines available). These were among the first games fully utilizing 3D-accelerated graphics back in the day, so they pushed boundaries and they brought the pseudo-3D games like Doom 1+2 into a full 3D environment.

• Baldur's Gate 1+2 + its expansions (remastered version available). Also highly recommend version 3 of course but that's not an old game. Plenty of mods available for them as well. These are all exceptional RPG games with great story and depth that no RPG fan should skip. They also age well because it's just good 2D art.

• Planescape: Torment (only if you a) liked Baldur's Gate and b) don't mind reading (it's a lot of text) and enjoying a complex story with complex character interactions. Remastered version available)

• Half-Life 1+2 (instead of HL1, play "Black Mesa" which is a great modern remake (not the same, but very similar and much better nowadays). For HL2, there are also some remastered versions or mods available, and Valve updated the game engine from time to time so when you download it today, it's not the dated version from 2004 anymore). HL1 (1998) was one of the first FPS with a really great story line, voice acting, and stuff like that, which is why it pushed boundaries back when it was released. HL2 was just excellent overall and one of the first or the first game which introduced physics-based object manipulations, so it again pushed boundaries further)

• Sin Gold was a great FPS from 1998 that got brutally overshadowed by Half-Life 1, but it's still a great story-based shooter, more action-focused. Based on an updated Quake 1 engine.

• Portal 1+2. Best to play them after you've played the Half-Lifes. Portal 2 (2012) is THE highest rated game on Steam (https://steamdb.info/stats/gameratings/). Truly great puzzle FPS set in Half-Life's setting, which is why it's useful to know about HL before jumping in (but not a requirement). Portal 1 also isn't far off in rating. Portal 1 was basically a "side game" for the Valve game compilation named The Orange Box, Portal 2 was then a true AAA quality followup because Portal 1 was a huge success.

• Deus Ex 1 (maybe. Graphics are really poor (they were already dated when it launched). But it was one of the first RPG-FPS with stellar level design and the freedom to approach every situation in different ways, so VERY good on the gameplay side). Deus Ex 2 is supposedly bad, so skip that. The newer ones like Human Revolution and Mankind Divided are decent but they're not classics anymore they're still """fairly recent""", around 2010 or so.

• System Shock 2. It also looks very dated by now but there are some HQ mods available (improving models and textures) which make it more bearable. I'm hesitant to mention it because it relies a lot on immersion and it looks very dated. So according to my own recommendations, I probably shouldn't list it, but it's also great in level design and gameplay, and its art style never was ultra-realistic to begin with, so I'll list this one as an exception. It's very much worth playing, truly a great sci-fi/horror RPG-FPS and a worthy successor to part 1. Nightdive Studios might be working on an SS2 Remake or Remaster, if so then I'd say wait for that!

• Monkey Island 1 + 2. Remasters available. Classic point-and-click adventures, timeless.
• There are even more great adventure games from LucasArts or Sierra back in the day, but you'll have to figure them out for yourself. I will only recommend Monkey Island because they were probably the most successful and well-known ones. For some of them, remasters are available, or you can play them using ScummVM. There were also other great adventures not from LucasArts or Sierra, like Simon the Sorcerer. The 80s, 90s and early 2000s spawned a lot of great point+click adventure games.

• Diablo 2 (remaster available). D1 started the whole "genre" of hack&slay action RPGs but it's rather poor in comparison and aged terribly, D2 is much better in all areas, so skip D1 and instead try D2.

• Z (very unique and fun RTS game from the 90s. If you haven't played it, you should! It offers very good and unique gameplay that no one else really tried to copy as far as I know, which is a shame. It truly emphasizes unit production time, speed and good timing). It's also entertaining. And difficult.

• Thief Gold + Thief 2 (remasters available I think, but even if not, despite the graphics being very dated, a lot of it is in shadows anyway and IMHO the general art style kind of ages well, though that may be subjective, and it's also immersion-based, so YMMV, but I think it's fine still). Also "The Dark Mod" as a community "continuation" of the series). If you like stealth FPS, you must play them. Thief 3 is also decent. Any Thiefs after that are terrible. There are amazing community-made mods/missions as well.

• Alien: Isolation. This one is from 2012 I believe, so not quite old, but an honorable mention because it's also an amazing stealth-based game. Its art style (like the first movies) also makes it age better. In fact I'd say this is one of the best horror-based stealth games ever made.

• Heroes of Might & Magic 3 (I think in this case, the remaster is bad. Stick to community mods/patches). This one is still the best of the series, so you don't need to play any other part. Ages very well because it has very beautiful 2D-based graphics. Great art and design overall.

• There was one old RPG which supposedly aged very well but I didn't play it yet. Maybe Albion or Lands of Lore, not sure what it was.

• Tomb Raider 1-3 (remaster)

• WH40k Dawn of War 1 is great if you like the universe and RTS games in general. Also the best in the series.

• XIII (Thirteen) - but not the new remake, play the original. It's a rather unique stealth-based, comic-look based FPS. Ages quite well because of its unique look (utilizes the kind of shading like Borderlands)

• Elder Scrolls 3-5 are very good as well but you need several mods or engine enhancements, otherwise graphics aren't that good anymore, and these are games which rely on good graphics as well for atmosphere/immersion. So they don't age well by default, but thankfully they have a VERY active modding community which keeps these games alive. You can even make them look very modern, but it takes time and effort to do so.

• Nethack (somewhat of a nerd game, terrible graphics by design (text-based art style), but amazing and very deep/complex gameplay, very rewarding to get into, if you don't mind its presentation. In terms of gameplay depth it brutally outclasses most games on the market). There are also some other clones like Slash'Em which I didn't play. Dwarf Fortress is probably similar in depth and presentation (but very different in gameplay and general type of game) but I also didn't play it yet. If you know enough about Nethack it's also not that hard, but getting to that point is very difficult and if you don't know anything then it's very difficult. (I've done 8 ascensions, i.e. 8 finished playthroughs).

• Honorable mention because it's technically not old but looks old: Return of the Obra Dinn. Don't skip this one, it's one of the best games I've ever played, I'm not kidding. It's truly amazing, and it's made by 1 guy. It's a perfect example of why graphics fidelity in games doesn't matter that much and you can create excellent, modern-feeling, stylish games regardless.