If you like rogue-like then Cavern is great.
Coming out this week if you like SRPG then Kingturn is the best game this year so far IMO. (Been playing advance promo copy for the last few days).
I think it's coming the day after normal release day like Friday for some reason. It really is a cut above the average IOS offering. It has a well written narrative, beautiful art, adjustable difficulty and enemy spawn rate, and 67 scenarios of pure SRPG goodness.
These two are great one thumb games where simplicity of control doesn't mean you lose out on great depth and gameplay.