Cute concept, I really wanted to stir up the rocky brew I had concocted by the end of the level and take a sip... haha.
As a few others had noted, I found it quite diffuclt to make proper defences as the 360 degree environment was pretty hard to see, and I felt too slow to get to the other side in time.
Nice idea for a defender game though, could certainly see something of this ilk get bulked up into a full game.