Not a fan of the Lucasarts adventures? My favorite is probably Indiana Jones and the Fate of Atlantis. Or maybe Day of the Tentacle... well, I don't like picking favorites.

edit: ok, here's one that isn't mentioned before (I think):
https://www.mobygames.com/game/dune
Not an easy game, but I finished it, probably in '95.

Geneforge. It's both indie and as classic as you can get, the whole series is on sale for less than 15 dollars when fully priced. One of the very few RPGs with truly unique settings, great writing and really anything you could ever want minus shiny graphics.
Honestly superb.

Link: https://www.gog.com/game/geneforge_15

Like Exile/Avernum it had lots of reworks, the original being pretty old. Not a DOS game, but you'll have probably missed it (being it fairly obscure), and not advertising it would be a shame.

Sacred2 Gold Edition

Master of Magic - Fantasy version of Civ basically.
Heroes of Might and Magic 2-3
Ultima 7
Day of the Tentacle
Loom
Beneath a Steel Sky
Cannon Fodder - Might wanna go with the Amiga version, it's a bit easier and sound is better
Star Control 2
Theme Park
System Shock
Star Wars: TIE Fighter
Warcraft 2, Diablo and C&C 1-2 (obviously)
Caesar III or Pharaoh
Settlers II
Dungeon Keeper
Lords of the Realm II
Star Wars Jedi Knight: Dark Forces II - TPS/FPS hybrid w/ platforming and minor RPG elements
Jazz 2 - Platformer
Lode Runner: The Legend Returns - Platformer. There's a nice, free fan remake of it

have to reiterate what others have mentioned already.

Lands of Lore, Beneath a Steel Sky, the entire Gabriel knight series, the entire Tex Murphy series,Grim Fandango, Gemini Rue are the gold std list for adventure games


ill let others vouch for the rpg ones

I can add Monkey Island 1 and 2 to that list, you can use classic graphics for the original retro feeling.

Yes! Yes! A thousand times yes! I was introduced to the series with #2, which is great, but #1 is incredible. Definitely a favorite of mine.

Thanks for the suggestions all, there's some I had already like the lucasarts games and Tex Murphy (which I haven't played yet), and some good suggestions of ones I haven't heard of. Not a big fan of dungeon crawlers or diablo-esque games, but I appreciate those suggestions too.

Series?

Yes, Neverwinter Nights; if you haven't already, you might check out some of the mods for it, particularly: A Dance with Rogues, and the Almraiven series. . . but definitely the cult-classic, A Dance with Rogues. Some of the mods for NwN were better than vanilla IMO.

Yes, nearly all LucasArts titles (even so far back as Rescue on Fractulus and Ballblazer) were/are cutting-edge.

Adventure Games: If you can find it, I highly recommend Obsidian. . . nice story and fantastic artwork. . . solutions are not ridiculously abstract.

God-games: I really enjoyed Black and White, and the Creature Isle expansion for it; I thought it had good art and fun/unique game mechanics and game play.

FPS: #1 on my list, even today: Realms of the Haunting. . . great story, really good FMV (no, seriously), very atmospheric, really good ambient sound, good art.

RPG: As far as story, sound, art, and atmosphere go: VtM: Bloodlines; best NPCs ever. . . lol. . . especially nurse Vandal. I might also recommend Gothic I & II; I thought they were fun to play as well. And, well, throw in Evil Islands: probably one of the most challenging RPGs I've ever played, but still fun.

Rogue/perma-death: lol, probably doesn't get anymore hateful than Starflight I & II. . . great games though.

Stealth: all the THIEF titles: great protagonist characterisation (Garrett), good art/sound and ambience, good stealth mechanics, good story.

Ah darn. I read "Imperialism." Doh!

Thank you, I made a mistake by putting Lands of Lore into rogue-like genre. Corrected just now.
OP specifically mentioned Krondor and Icewind Dale games: "I already have the Krondor games, Icewind dale, Neverwinter and Demon stone, but would appreciate any gems I might be unaware of.".

Trying to think of some stuff that's more obscure and I'll say try Blue Force. It's a neat little 80's nostalgia trip from the Police Quest guy, and a solid adventure game iirc. Also Blade Runner if you haven't played it. Quality adventure games, both of which are total abandonware, and work with ScummVM.

Woops. By the time I went through the proposals till then, had forgotten what the OP said and then just checked the list.

For game's like Gabriel Knight there was Gray Matter but that disappeared from GoG and I don't know if they're getting it back.
The Black Mirror is another one.