Breja: TRON 2.0 is still one of the best FPS games I ever played.

Same goes for SWAT 4.

Diablo is a no brainer, for me it's still the best hack'n'slash ever made.

Unreal is surprisngly great. I have not played it back in the day, only once I got it here and although the graphics sure have aged, the gameplay and atmosphere are still rock solid.

The gameplay of Armed & Dangerous on the other hand isn't exactly fantastic, but it's still one of the funniest games I ever played, and there's just so much humor in both the story and the gameplay (land-shark launcher!) that it's still a blast to play.

Indiana Jones and the Emperor's Tomb - plays something like an early Uncharted before the actual Uncharted, and it's a very solid use of the movie license. The only drawback are some frustragin levels near the end and a lackluster final boss fight. But if you like Indy or just action games like Uncharted and Tomb Raider, it's still quite good.

Judge Dredd: Dredd vs Death - this one is nothing great, but sometimes you may just want to play a simple, solid shooter without any bells and whistles, or overlong complex levels. Just go and shoot and have some fun.

Robin Hood: The Legend of Sherwood - ok, so this maybe doesn't fit the genres mentiond by the OP, but I just can't hel listing one of my personal favorites. It's basically Commandos but in medieval England, with Robin, Little John and all the rest. The graphics are still beautiful in my opinion, it tells the familiar story well, Robin's adventures translate to this kind of stealth/tactical combat hybrid perfectly, you get to run your Sherwood encampment in between missions, and it has the super fun mechanic of actually controlling any characters movements in melee combat with your mouse, making for great duels or epic scenes with holding back whole squads of guards with Little John.

Rhalius: Dungeon Siege holds up well, the first one especially, second one is alright and the third one is garbage.

But that first one is a great hack and slash game, pretty simple but you get a party of eight to control. Music is great, there are no load times and the stages along with the music gradually transition into new areas, and each area seems to last just long enough, some maybe slightly short even but they never outstay their welcome.
Also this game has an insane loot list.
First RPG I ever played, spoiled me for the future since even the 10th play through I'd find items with appearances I never saw before.

Dungeon Keeper 1, also still an amazing game. The sequel is good too, but the first one is great. Really has a great art style and atmosphere, the second aged poorly due to early 3d graphics and a more cartoony art style, as well as creatures not feeling very powerful when levelled up and casters being weak.

Casters in Dungeon Keeper 1 really is something else. They throw up shields and toss spells like crazy, really feeling like they go all out.

Fortuk: Can't go wrong with Deus Ex in your chart.

Lots of good games already mentioned. Sacrifice and Outcast especially are great games that are usually underrated.

Planescape Torment
System Shock
Star Wars Republic Commando
Painkiller
Psychonauts

A bit closer than mid 00 you get

Hitman; Blood Money
S.t.a.l.k.e.r
Mount & Blade
Pathologic
The Void

If you end up trying Fallout and liking it, there's also Underrail as modern rpg with relatively modest system requirements.

People already named Jedi Academy, but all of the Jedi Knight games are pretty good. Star Wars Jedi Knight Dark forces II and Star Wars Jedi Knight Jedi Outcast, especially.

dtgreene: How about Wizardry 8?

brysmax: I have Arx Fatalis and actually just started playing; is the Arx Libertatis port the way to go for a first blind playthrough? I thought the game looked pretty good.

amok: Psychonauts

Leroux: Hm, no idea, I think I played it unmodded, maybe even shortly before Libertatis came out, but not sure. I don't remember having any performance issues or so, in any case, and I very much enjoyed the game and its atmosphere.

Leroux: Was going to suggest that, too, but didn't, because I think it's already available for Mac as well?

Another candidate I didn't mention because it has a Mac version is 2001's Return to Castle Wolfenstein (And also because I couldn't link to it since it's blocked on the German storefront... XD)

brysmax: Holy crap, rly? Is that true for all Wolfenstein games in Germany? RTCW was awesome ill see if it’s on sale.