Really fun, but can be improved.
The game really entertained me, and is really original in concept. I haven't played a defense game Quite like this. I love how the AI actually gets out of the way instead of standing there like an idiot.
However, there is room for improvement. The artwork was pretty good, but the animation felt stale, which is a common problem with flash. Games like The Last Stand has worked around this problem, however, so it's possible. My biggest problem is the prices. Even the earliest items are expensive, and it's hard to get by only buy one or two objects, as the difficulty progresses quite swiftly.
It is overall a good game, I would love to see some kind of sequel, perhaps with some story development and whatnot.