I'll second Solomon Kane, and also say I want a real Conan game.

I've always thought a Mike Hammer beat-em/shoot-em-up would be fun. Just a nasty, mean-spirited, violent game.

John Carter of Mars.

Elric.

People always wring their hands over how to do a Superman game, but I think a point-and-click adventure would be great. Just use your variety of powers to solve various puzzles and tests of morality and ethics. Which is basically what DC's superheroes were before everyone got so preoccupied with making them punch everything all the time.

Oh right I forget there were two. Definitely the more light hearted US version I think.

If we're talking 80s cartoons, I always liked Visionaries. The show is very much a product of the time, but I think the setting is honestly very interesting and it's all very visualy unique. Whether as a game or a new show, it could make for something really special.

I'd love to see some of Jack Vance's work adaptations. Cugel's Saga would make an interesting adventure game.

Yes!!!

I guess you meant an adaptation more faithful to the original Germanic setting?
Because Wagner's Ring cycle treatment of the Nibelungenlied poem already got turned into a game in 1998.
All in all three games actually, including a text adventure from 1993 and a 1996(!) open world FPP/TPP DOS adventure/RPG-lite from Psygnosis. I raise you Galaxy Rangers.
Or anything taking place in the criminally underused Sci-Fi Frontier setting. Although ExeKiller looks like as if it might scratch that itch, at least in part.

Idea: An RPG based off of Isaac Asimov's Foundation series.

The gameplay would be similar to that of the SaGa Frontier games. I'm thinking that the growth mechanics would be like SaGa Frontier 1, while the overall structure would be like SaGa Frontier 2, where you pick individual events to play. (One difference from SF2 is that the playable events would be at different locations in the galaxy.

Edit: Why the low rating?

Yes. Playing through Skyrim, God of War, and various Lord of the Rings games really got me to wanting a "straight" adaptation.

I knew of the 1996 game, but not the earlier Ring Cycle. Interesting.

Midworld by Alan Dean Foster

You actually gave me a serious reply, I was going to suggest a Computer Chronicles quiz kit where you try to predict what the host is going to talk about based on the product, and if it actually made a real impact or was relegated to the dustbin of history.

Games based on Asimov books would be great.

Still waiting for a proper character-driven open world RPG adventure in the Warhammer 40,000 setting.
Basically The Witcher but centered around a prominent figure like Gregor Eisenhorn or Belisarius Cawl.

Also a concept from the W40K universe that I think would lend itself really well to a game adaptation is Genestealers resp. Genestealer Cults slowly infiltrating, secretly rising up within and trying to take control over Hive Cities.

The turn-based gameplay would consist of strategic macro-level management via a Frostpunk-like top down view on a Hive City and go through multiple stages or generations, starting with the concealed arrival of a single genestealer, spreading/reproducing/creating more human-looking hybrids, further concealing themselves by forming an organisation like yet another cult in the name of the Emperor, embedding agents in key positions of the Hive City's governmental structure, and then ultimately, upon receiving the approaching Tyranid hive fleet's signal, reveal themselves and either completely overthrow and take control of the Hive City or cause as much diversion and disruption as possible until the hive fleet's arrival.

Legend of the 5 Rings would be a perfect setting for a RPG, MMORPG, or a Total War strategy game.

I want Owlcat's next game to be based on Starfinder rather than Pathfinder.
100%. Asian-Fantasy family-building TBS, please. (But not all in on the "grand strategy" games. But mythic hero units and loyalty.)

Another of my favorite novels, Bruce Sterling's Holy Fire, would make for a great close in 3rd person RPG. (Basic premise: Very old woman in the ruling class once society is a gerontocracy gets life extension procedures, including making her brain think young. She has shock of youth vs being a member of the gerontocracy.)

(Basically any of his novels would make great narrative games. Heavy Weather, a story about chasing post-climate-change superstorms? Yes.)

Honestly, while I enjoy it greatly, I feel like the Germanic/Norse mythology and folklore have been done to death in games. What I would love to see is a game based on Irish lore. Whether it would be the Ulster cycle and Cuchulainn's story, or the Tuatha De Danaan's wars with the Fomorians, or the Fianna cycle, there's so much material there I'm amazed it remains almost entirely untapped. And it's influence on our modern fantasy has been tremendous as well, just not nearly as broadly advertised as the Germanic stuff.