Fun game, I found it very addictive. I've never been very good at games like these, I only got to level 5 - 89%.
As Styxdrifter said, if you make any more like this, make more varying obstacles, not just the same 4-5 over and over.
This game is really fun, but ends up being very easy (at least, on defence mode). It's difficult for the first few levels, until you get a machine gun (this is what I got).
The SCAR makes the game far too easy, as the gun does lots of damage, and reloads really fast. Is it supposed to only have a 0.4 second reload time?
Also, since there's so much blood on the ground later on, it gets really hard to see the red coloured enemies, and the constant shaking from gunfire doesn't make it any easier.