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.
Definitely the mobile version of Stardew Valley
Slay the Spire is excellent on mobile, it’s a roguelike deck builder.
May be the commercial one but actually Candy crush is a nice one
I work at a gaming company - Candy crush is known for employing the same tactics that keep people sitting at slot machines for 8 hours a day, and every damn PM wants to copy those patterns.