I've been playing UFO 50. I fuckin love this game. I second basically everything said in this glowing review:
Collection of 50 new ’80s-era game concepts brims with originality, care, and joy.
arstechnica.com
The basic idea is that you've discovered an old NES cartridge made by devs (UFO Soft) who happen to have some knowledge of modern gaming design. Within this cartridge are 50 games they made between 1982 and 1989. Games that were made "later" are influenced by earlier games. There are some direct sequels. All of the games are limited to the specs of the NES. And they are 50 FULL games, one of them is an RPG that would probably take 60+ hours to get through.
And that's it. There's loads more easter eggs of course but read the review. I aimlessly picked a few titles at the start that I though sounded cool (Warptank!). But now I'm going from the beginning.
Also I'm tagging
@VashTheStampede because it seems like it would be in his wheelhouse.