I love the art style this game has, but its setting seems to be the only thing making it interesting.
The heavily styled graphics are well done. Though all the characters are small and dressed in a similar way, you can always make out which enemy is which. Everything else is easy to make out as well, even with your restriction to a (mostly) gray scale color scheme. I enjoy the urban landscape all the levels take place in and the neon light at the end was badass.
The sound is a mixed bag. The shotgun and Thompson sound very powerful in both firing and reloading. Boxes also sound very satisfying when they break open. The enemies sound fairly uninteresting overall. The copy/paste "ARGH!" doesn't really do anything in the way of satisfaction, though the guys in stripey shirts are a bit different. Their echoing scream explosions and eruption of coins and shotgun shells work pretty well, though it still feels almost as stiff as the other deaths. The music's blend of jazz and 8-bit is awesome and I'd love to download the tracks if it were an option.
My main criticism with the game is its core gameplay. As a basic platformer it's very competent and well executed. Everything is perfectly responsive and tight. However, being a basic platformer also makes the game a bit stale and uninteresting. There's no real special mechanic to set this apart from any other well made sidescrolling shooter and I personally feel the oomph of using the guns against enemies isn't satisfying enough to pull the half hour it takes to beat the game off. It's nice you made the levels mildly labyrinth-like as oppose to staying on a left to right spectrum, though. I like the vending machines throughout the game, though as I got further in I saw there really wasn't any need to use the $20 machines when the $5 one's ammo and health came out so frequently. The game's also pretty easy. I didn't die a single time, even on the final boss. I think the life bar is a bit excessive, then again as another Flash gamer put it, "Who wants to lose at a Flash game?"
The story's obviously thin, but it serves its purpose. Though the set up doesn't really justify everything that happens.The cutscenes are a decent break from gameplay and I like how they were utilized once or twice to give a heads up about new enemies.