Play it to the end, people....
First of all, the glitch with the "Old Glory" is just a problem on your computer, cuz it works just fine for me (xD). And if you'd just play it to the end (lvl 40), you'll get an even better weapon, "Fisty McBeefy" or something. Essentially this is a huge, paper-mario style fist that drops down on command and pounds the ground, killing nearly everything on-screen (depending on your aim) in one hit. Personally, I believe, though this is an old style of gaming, the addition of such a weapon makes it truly a commendable game.
Oh, by the way, the gravity gun DOES work on tanks, it just takes 2-3 shots. It's quite funny, actually, as the tank's ripped apart, then flies into the air XD
Great job, keep 'em coming.
~Booored