This idea is not new, i've seen it been executed a LOT before, i even saw multiplayer duel versions of this, when this has been said however, there's nothing specially bad with the game.
What i do however not like, is when you write, and i quote: "The game sprouted from an idea my friend had that was pretty much him just saying "Dude, imagine pong, but in a circle." Obviously I've expanded that idea into this"
First of all, by using teh word "just", making it seem like he didn't come up with much of an idea, i can only suppose you do this, because you refuise to accept that this is his idea, not yours, and that doesn't seem nice, to a person, giving you an idea, never use the word "just".
Second, you say you "expanded" it... you didn't, this game doesn't contain more than that basic idea, really...
I thought about giving you a lower score, for being such a jerk, but i don't think it's fair to the game, which by all means, is decent.