Awesome!
The graphics o this game were superb. Light angels and everythign were brought into consideration. Enemy character models looked good, with the exception of stickmen. Even the gun shots looked good. Even small details like the tanks barrel moving back after firing was included.
Everything was animated fluidly and no matter how full the screen got, it hardly ever lagged. Now that may just have been my computer, or it good have been the simplicity of some of the animations and graphics.
The gunshots, explosions and other miscellaneous sound effects were very good. The only noise I had problems with were the noise your own gun would make, with the exception of the gravity gun, which sounded really alien like.
The descriptions of each weapon were also fun to read. I liked how you included a bit of background information to bring it all to life. However, ti would have helped if you gave a description for everything else as well.
The violence wasn't all that detailed, just a red mark and a few explosions. Still, it would have been kinda slow if there was more detail so maybe that was for the best.
The controls were very simple and easy to use. Just a click of the mouse and a tap of the spacebar. It helped that everything was so simple. If it hadn't been then things would have gotten messy pretty quickly, I'm sure. The upgrade menu was also simple. It also looked nice.
There were also many strategies and options available to the player, and I'm sure it would take many days to figure out them all and how to use them to their best efficieny. If there's one thing I like in a game, it's having more than one option when dealing with a problem.
I hope you continue to make more games like this, improving and giving wider arrays of weaponry to choose from.
You may also want to try it the other way round as well. Where the player atacks the house.