Isle of Arrows is a near perfect mobile game and the best $6 I've ever spent on the Play store.
- One handed vertical
- No ads, no mtx
- No in game currency or bonuses or powerups
- No daily or weekly check ins
- Campaign with a beginning and end
- Can pick up and play for 1 minute or an hour
- Great art, simple but wildly fun tower defense
- Dozen of permutations to gameplay during the campaign so it never gets repetitive

Do yourself a favor and grab this. Might be my favorite mobile game ever and I wouldn't uninstall it with a gun to my head.