I was about to comment something else, but then I read the description again and it made sense.
Anyways, It's an interesting concept for the game. My only complaint is that the time it takes to swap between weapons is too long. It's nearly double the time it takes to fire a second time normally, and even that is on the verge of being too long.
I also don't think there's enough incentive to move exactly two spaces. Yes, the weapon becomes more powerful, but to maintain that bonus, you have to move two spaces again. Instead of shooting, you spend your time moving around the board, trying to get the weapon bonus, and hoping to god you don't get the shotgun weapon, while moving more than two spaces, or less for that matter, is still fairly powerful.
But otherwise, It's a fun concept for a game! I ended up with a high score of 126.