A lot of really good older games have been ported to mobile and work fantastically. Knights of the Old Republic, Neverwinter Nights, and Baldur’s Gate just to name a few. Hell, you can play Baldur’s Gate multiplayer, cross-platform with PC players even! There’s also fo2.exe on the Play Store, which lets you play Fallout 1 & 2 on mobile provided you have access to the files from the PC versions. Oh, and Doom ports galore, of course.
As far as mobile-only or mobile-specific games, my favorite is probably Caves, a surprisingly well done and completely free roguelike.
Slay the Spire is excellent on mobile, it’s a roguelike deck builder.
Might not be the answer you expect, but I have an iPhone and I got myself an Apple Arcade subscription without expecting much (I didn’t play mobile games at all before that, because they tend to feel either unoriginal, or scammy, or both), and I was surprised at how most games (not all games, but still) were truly original, and none of them were scammy since I was technically paying for them with the subscription. It’s been a surprisingly nice exploration.
Marvel Snap is a really fun lightweight TCG kinda thingy. I never liked Hearth stone or Runeterra, however I thoroughly enjoy Snap
Cytus II, it’s a great rhythm game with a cool storyline
