I played this game solo, so take that into account when reading my comment.
I think the concept of the game is fairly interesting, and with some extra polish, could become a fun game. Most of the simplicity works in favor of this, including the objective and graphics. That said, I also think it was too simple, and there were many parts where I think changes would be necessary.
On first impression, the color-coding of the game was really confusing. I'm used to lighter colors being closer to peripheral view: therefore, my interpretation was that lighter parts of the map = mountains. Obviously, I ended up being surprised it was quite the opposite. I also found that since both player 1 and 2 look exactly the same, it was easy to confuse which was which. Furthermore, it was hard to keep track of which player was winning, since my focus was directly at the player's position instead of the upper-right-hand corner of the screen. It would have helped if instead, there were a P1 and P2 marker, along with their score over each ball to make it easier to track these information.
I also I think the objective of the game, to get to the lowest point of the map, is too easy and anti-climatic. Once a player has reached the lowest point of the map, it's actually quite easy to defend, since if they "slip," they can just roll back down to the same spot. This often made the map the biggest determinator on which player won: the player closest to the deeper valley almost always had the bigger advantage. While the theme was "deeper and deeper," I actually think this game would have benefitted if instead, the objective of the game was reversed: getting into higher elevation scores higher points. In this case, there's a very real tension for the winning player to defend their spot: a small mistake could very much cause the player to lose balance and fall down, making way for the second player.
Lastly, adding at least one more power would have helped. When two players are fighting over the same ditch, it just feels like a casual bumping match. If, for example, a "boost/tackle" button was added, that could make the game more competitve.
There's some potential with this idea: would like to see a more improved version of this game!