These are some of my favorites that you can pay for once and play forever (all on Android, I think most should be on iOS too)
Ticket to Earth: Innovative puzzle RPG, crazy amount of content for price
Sneak Ops: Casual version of old Metal Gear stealth (f2p but you can pay a 3.99 premium upgrade)
10000000/You Must Build a Boat/Zookeeper DX/Triple Town: Match 3 RPGs that aren't riddled with iap (Triple Town is f2p but you can also pay a 3.99 premium
upgrade)
The Battle for Polytopia: Tiny version of Civilization (this one is actually f2p but you can pay to unlock different tribes, I still haven't though)
Pocket City: City builder (I think it has a free demo?)
Tennis Superstars: Surprisingly deep tennis game you can play with one hand
and then some good ports are Game Dev Tycoon, Rollercoaster Tycoon, and Crazy Taxi (f2p, pay to unlock ads)
For f2p games, Gears Pop/Clash Royale are fun but the monetization can be frustrating