Nethack/Slashem too in case of Roguelikes. Nethack adds tons of Terry Pratchett references as and homage and it's cool but Slashem has tons of weapons, classes, objects, environments... And supertux2 has both the main campaingn add tons of downloadable ones too.

Ditto with Oolite, tons of community content.

Shattered Pixel Dungeon it's a fork and still has tons of contents and it might be the most playable FLOSS game in Android among Unciv. Oh, and it can be run on potatos.

Sometimes you don't need AAA graphics.