Originally Posted by Appletini
In addition, the temporary vehicles change the nature of the run for a time, and the missions always give you an alternate goal to work towards.
Oh yes, and achievements which also serve as "missions". By this I mean they require you to do something in-game, other than "run 2,000m"
The only downside (sorta) is that there's nothing I really want in the coin store. Sure, there are plenty of things to work towards and I'll get them all, but nothing immediately jumped out as "I must get this".