A similar game to Threes is 2048. It's essentially a puzzle game that has you swiping to shift tiles and match numbers to create larger numbers, doubling them by two and hopefully getting up to 2048 if you're good.
It's an easy game to play and the learning curve is low, but it's difficult to master. However, it's a game that you can put as little or as much energy into it as you want.
It does take a bit of strategy, though, as starting out is plain and simple, but as you get going, you'll want to be strategic about where you slide tiles to and which ones you match up, because one wrong move could bite you later on in the game.