Close but no cigar...
Well, this game is what it is. Not a bad representation of the genre. My only complaints have to do with the lag and the upgrades. I honestly think this would be a lot better without so many graphically intense explosions. Arrows should not make that big of a bang when they hit your base. Some of the "fireball heavy" levels were so laggy it took almost 20 seconds to reload my gun.
As for the upgrades. It seems like a lot of the later upgrades were less effective than the previous ones. Case in point: The sniper rifle compared to the machine gun, and the lightning effect compared to the explosive effect. Maybe up the damage or decrease the delay?
Oh, and it's just my opinion, but you guys should really get a second song. I can't count how many games I've heard this track in.