A very amusing entry and probably the most fun game of hot potato I've ever played! I was giggling like a mad-man while running away from grenades and laughed out loud the first time I got to the the game over screen!
I made it to 6 waves remaining with a score of 4415. I liked the escalation of difficulty and the gradual adding of more obstacles and mechanics to keep it interesting. A GUI indicator that I'm close enough and pointed in the right direction to grab a grenade might be a nice touch - sometimes they were just out of reach.
My ratings for graphics and audio are low only because it's not clear what you made yourself and what was existing free content that you used - the overall effect and atmosphere was great.
Good job for a first entry and hope you keep on making games!