Fun game.
Well, I'm on level 35 right now, an hour and some change later, with full upgrades, and 101 soldiers, etc., so great job on making something rather addicting. Loved Defend Your Castle, this is a great addition to that genre.
One glitch I saw, though; occasionally, there's a dude that randomly can't be killed and just keeps running straight off screen. Other than that, nice little game here.