Short, sweet and fun! What I really love about the melting snowball is that it isn't just a time limit for the level, the ball being smaller also provides opportunities to use alternative paths or just get through obstacles more easily. This creates a really satisfying risk/reward sort of system where waiting out the timer a little can actually be good but overdoing it will cause you to fail. It also naturally creates this system where the game gets a bit easier if you are doing poorly, kind of like a dynamic difficulty.
Having the snow pick ups grow the ball bigger again provides has a ton of potentional for interesting level design. But speaking of the pick ups, on one level I found an oversight, if you quickly fire through the course while the burners are off, gathering all the pick ups this happens:
The ball gets giant, stuck in the walls, and you get blasted with the collision sound. Have to a wait a while for the ball to shrink before you can continue playing. So you should probably put a max size limit on the ball or something.