Grimvalor is a pretty good Castlevania style game. They managed to strike a nice balance between making something that’s more complex and immersive than typical phone games while still making it play smoothly with touch controls.

The Star Wars Knights of the Old Republic games (Bioware RPGs from the golden age of Bioware) are also available on iPhone. I’ve only played the PC and Xbox versions so you’ll have to look up reviews to get more information on what the ports are like. Some of the recent reviews on the app store say it’s buggy but I don’t know how bad it is.

Night in the Woods (story focused walking sim), Inside, and Limbo (minimalist puzzle platformers) are others I’d recommend, but like KOTOR I played them on PC/console so you’ll have to look up reviews to know whether the iOS ports are any good.