Could be fun.
The game itself is really smooth and pretty addictive. There are just some things that need improvement:
Music and (more) sound effects would be nice. Automatically restarting the level when you're out of balls would also be nice, so that I don't spend 30 seconds madly clicking because I can't read. The "ball left", "level", and "score" font not being Times New Roman would be nice. A pre-loader would be nice (maybe there was one, but it didn't seem to work). Making the tank move with the mouse, so that you only need one hand, would be nice (of course, that doesn't take into account people with laptops, but you could work something out).
The hard part - making the game itself fun - is definitely ready. It just needs a little cleaning up is all.