It would be interesting to see a DooM (2016) anime.
Marvel Land by Namco (Arcade/Mega Drive), Ghosts 'N Goblins, or Magician lord. But, Doom series would be awesome, too : )
Asuka 120% BURNING Fest., Mad Stalker: Full Metal Force and Panzer Bandit.
The star ocean series. Kingdom hearts
Definitely Sword of the Stars. It would make a pretty cool like space anime.
Threads of Fate, just for being a sentimental favorite that deserved to have an existence beyond just one game (especially since the ending cockteased the fans with the promise of a sequel).
I definitely agree with Zelda. I'm surprised it's never happened honestly. While I know one exists, I wouldn't mind seeing a new Fire Emblem anime.
Metal Gear Solid. :D
Beyond Good and Evil would probably make a pretty neat anime.
It would definitely be awesome to see an anime about DOOM, an anime about Wolfenstein, and an anime about the Heretic & Hexen series. Sadly, the chances of this happening are highly unlikely, and there are far too many asshats in those fanbases who would probably do anything to boycott such ideas from becoming reality even if some animators were to decide to actually work on those ideas and if the original creators actually gave them the legal rights to proceed.