The obvious answers would be GTA3, The Bard's Tale, or Aralon which are all great games well worth their asking prices. Check out Mission Europa. It's an immense first person RPG-esque game. It's definitely a hidden gem of the app store.
Newest one: Nihilumbra Seriously, check the game out. Expecting a 5-star review from TA very, very soon. http://forums.toucharcade.com/showthread.php?t=142440
If you like JRPGs the chaos rings series by Square Enix/Media Vision is by far the best on the app store, the whole series cost £30 though I recommend just getting chaos rings II for £13 which is well worth it if you don't want to spend too much. For WRPGs Aralon by Crescent Moon Games is the best, although if you prefer MMOs you might want to get order and chaos by Gameloft. Dungeon hunter 2 by gameloft is also a decent Diablo clone.
