Chain Dungeons is a free RPG with puzzle and action elements. It'll be familiar to anyone who's played Candy Crush Saga or similar puzzle games, and it builds on those familiar ideas with a fantasy setting and heavier RPG elements.
Easy to play, very tough to master
Chain Dungeons is a simple game. In it, you string together various puzzle pieces to ultimately perform attacks against your foes. A major focus of the game is setting things up so that when you do attack, you perform powerful and damaging combo attacks. Also a part of the game is summoning new allies and crafting items. This is fun in its own right, but it can take a long time to obtain new things, meaning that though you can play this game in short bursts, it may take a little while to make real progress.
Give it a yank
The basic gameplay of Chain Dungeons is generally satisfying, and the game is worth checking out for anyone who wants a simple pick-up-and-play RPG on their phone. It can be difficult after getting started with the game to progress, but the ideal Chain Dungeons player is willing to put in a lot of patience and dredge up a little luck to get ahead. If you find yourself really enjoying the game, invite your friends to play it with you: it even has co-op multiplayer.