Mobile games are masters at keeping you hooked, and, for the most part, progression systems are the main reason why. They give you a feeling of completion. They make you feel as if you accomplished something even though you've been grinding the game for a while. While some progression systems make it worth your time, some don't.
So, with that said, the following mobile games offer the best. They turn leveling, unlocking, and collecting into loops so satisfying it’s hard to stop playing once you’ve started.