Entertaining and challenging. I'll skip past the issues that everyone else has already brought up, with a single exception...
Perhaps you should ~tag~ this as a Demo and/or present a popup at the beginning of the game, instead of simply writing it in the Author Comments section (... which people will generally read after they've hit the glass wall, and are asked to buy it).
I might also point out that I consider Newgrounds as a place for struggling artists to make their work seen - but not neccessarily to sell them. Certainly - post whatever you like, but I visit NG largely to experience and critique... and not to buy. Being asked to, or having content restricted to paying players only is a bit of a turn-off, and may hurt you in the long run.
My advice: Work a little on the presentation, and kickstart this baby at Steam.com . That way, there's no tease. People will pay, and at the same time they will understand what they're getting. The rest of us want to be free.