FF games are a solid choice. The Pixel Remasters have been very well received and anything that makes the early games more approachable is a solid win in my book. That said, I personally found the 3D version of FFIII (actual 3, not 6) to be phenomenal.

Best feature in that whole game.

Seconded. I loved that game but that part of it honestly blew me away.

Aside from the other choices already mentioned (especially Doom stuff, FreeDoom ftw) any of the free games derived from the S.T.A.L.K.E.R. games and early builds, mostly Anomaly and Lost Alpha. There are also a few stabilized versions of the Build 1935 alpha out there which are worth playing and probably a bit more approachable for most people.

Oh snap, subscribing to that.

EDIT: well, once I can actually load it through lemmy.world.