I’ve been playing Pitfall.
It’s kind of fun, and unlike Temple Run actually gives a feeling of progression. Playing a game is not an empty, self-contained event as you can use the coins you collect to buy stuff (especially tokens that allow you to continue from checkpoints).
Since I’ll never pay a cent to a free-to-play game I highly doubt I’ll see the ending (if there is one?), but what I have access to is entertaining enough to keep me playing for now.