For such a simple premise I found my self having a lot of fun. There is a sense of urgency and sometimes almost a desire to see how far you can take your friend down the mountain.
Down the Mountain is easy to grasp, you simply tap either left or right to make your character jump, you guessed it, left or right. Tapping feels responsive and the character moves really fluidly.
The game level is comprised of standard simple blocks, which offer no resistance to the player, and special trap blocks, which force the player to do something to escape or simply kill them on the spot. It is oddly satisfying to see your character explode after standing on TNT.
The flow of water was an interesting block because as the game got more and more hectic I found my self needlessly plummeting down a waterfall with no way of stopping myself careering into a lone TNT block. As you collect stars in the game you can use these to skip levels you are struggling on.
For 79p you can remove the adverts, but the advert on my game was in no way intrusive.
The game has enough going for it that it will easily make the commute to work less arduous and you will probably find yourself playing this to pass a few minutes throughout the day. Everything is done in such a way that you can pick up play for a few minutes then resume in a few days.