In addition to a few I’ve seen posted already (Stardew Valley especially)…

• A Dark Room: A relatively short, minimalist, mostly-text-based RPG with a dark vibe. I come back to this at least once a year. Can be played free via web browser, but the native app version has some extras.
• Dysmantle: A huge and well-polished zombie survival sim. Just recently finished it and was really impressed with the overall scale, level design and progression.
• Papers, Please: A ‘dystopian document thriller.’ You play as a border checkpoint agent, verifying increasingly-complicated passport documents and questioning your moral compass. Port of a PC game by the same name.

Monument Valley

I HATE playing mobile games but my wife got me hooked on Dawncaster. It’s a roguelike deck builder. I think it’s like $4-5 and no micro transactions but there are expansion packs to add new zones and enemies. I’ve since picked them all up. It’s regularly updated with free content packs and balance changes. The devs are very responsive with the community.

I’ve got a lot of mileage out of Pocket City 2.

Slice and Dice: https://play.google.com/store/apps/details?id=com.com.tann.dice