I think there were tons of great videogames on iOS. Unfortunately, nearly all of them disappeared once iPhones moved from 32-bit CPUs to 64-bit.
My favorites would be Jeff Minter's Minotaur Project series. Minotaur Rescue and Gridrunner were my favorites, but they're all great and I miss them dearly.
More recently, there's an indie classic called Forget Me Not that's available on iOS once again, and I cannot recommend it highly enough. It's one of my all-time favorites, a beautiful mashup of a Roguelike dungeon crawler, a shoot-em-up, and a Pac-Man dot muncher.
PS: Fruit Ninja was good dumb fun, Jetpack Joyride and Age of Zombies helped to keep me sane on plane trips (I'm a big baby thanks to turbulence), and there was this one retro game where you were a kung-fu dog and you knocked down enemies that appeared to your left and right, just simple reflex action, but very addictive.
PPS: And, of course, who could forget this modern gaming masterpiece? This may very well be humanity's crowning achievement. Move over, Buzz and Neil!