The popular roguelikes game Dungelot is free for a limited time. Dungelot is kind of like Mindesweeper, but with a twist. Players must navigate dungeons by flipping over tiles to uncover treasure, and to find the golden key that unlocks the next level. The game also features an RPG element with turn-based battles, and the ability to collect weapons, spells and other helpful items. There are 5 different heroes to unlock with 15 different abilities to upgrade, and plenty of fun, cartoon monsters to fight. The game also offers leaderboard support and achievements.
The game has decent reviews, but I found it to be a little tedious, and it doesn't offer much in the strategy department. You basically just flip tiles and hope your health doesn't run out before you find the key. If you do die, you lose everything and must start over. The game is fine for a free download if you have few minutes to kill, but I wouldn't recommend paying for it.
Dungelot works with all iOS devices, and has been optimized for the iPhone 5. You can download it from the App Store.