What strikes me about Crossy Road's monetization strategy is that, although it is free to play, it does not force users to cough up in order to progress (as is common in most freemium games), as Dave Tach at Polygon explains:
Crossy Road also is free-to-play, but it avoids the pay-to-win hooks that have earned big-name freemium games a bad reputation in mobile gaming's gold rush. Players can pay to unlock a new blocky character to hop through the game, or they may watch short video ads to earn credit that unlocks the cast faster. Or they can simply play on without doing any of that.
Unlike many of its contemporaries, nothing about Crossy Road makes a player feel the need to pay to progress or win.
Implementing this business model has no doubt reduced the amount of money the developers stood to earn dramatically, but it has also made playing Crossy Road far more enjoyable and, personally, has allowed me to recommend it to friends freely.
The whole piece is an excellent read and should prove inspiring to aspiring mobile game developers.