Either fully free, or single payment, no in-between. Gachas and MTX are bad even if good, either for DRM, heavily addiction-oriented design, GAAS, privacy concerns, and so on.

Dandara is fun though pretty hard.

Quest of Dungeons is pretty good for short plays. Also dev's on Mastodon.

ConflictCraft, Defense Zone 2, LYNE and Downwell are good time wasters.

Anodyne and Ittle Dew are great adventure/puzzle games.

Deeper Down Dungeons was pretty challenging in a fun way, despite looking a bit like an asset flip at first.

The Final Fantasy franchise has several titles on Android, though be warned Square Enix loves to use DRM on their Android ports.

Also many games that can either be emulated on Android, or because of their underlying engine, can be unofficially ported. Games like VVVVVV, Aquaria if you can figure out how to compile the open source engine to Android or emulate the PSP port, Metal Slug 1 through 5 which in most releases come with working ROMs, RPG Maker and Ren'Py games through JoiPlay, and the massive amount of homebrews over at Itchio.