Almost perfection.
Here's the deal...
I've been visiting Newgrounds regularly for many a year now, and never until today have I felt the need for an account here, as I am not a Flash artist myself. However...
This game is so near to perfection that it might as well -be- perfect. The one thing that annoyed me only very slightly was the sound for the AK47, but that annoyance pales into insignificance next to the rest of the game.
I loved the weapons, throughout the game they all felt powerful and up to the task, and I loved the bullet drop. The other aspect of the weapons physics I found really interesting, almost turning this 2d game into semi 3d with the way you can spray bullets into different 'rows' from one position.
The zombies were pristine, from the detailed faces right down to their explodable kneecaps. Absolutely spot on. (And hilarious.)
The 'shopping' aspect of the game was excellent. All very well balanced. Using survivors instead of turrets was a brilliant move, and the extra healing power was much appreciated. I also liked that all the weapons had infinite ammo, which isn't suitable for many games, but worked very well here.
So all in all, this is THE best defense game I have ever played, and it's in my non-existent top 5 Flash games ever. I can see every second of the 8 months work you put into this, and is all the more impressive for the fact that it's your first game.
I just wish I could crank up the difficulty and do another 20 days with nothing but the final weapon...