I feel compelled to put this out there after having picked the game up on Steam for 50% off (so ~5 bucks thru the weekend). I started it up after getting in around midnight from the bar, thinking it would be good for a half hour or so before bed, and damn if it isn't near 6 am now. I haven't had an experience like this with a game in a long time; if you are an old school gamer this is simply something you must pick up.
It has an incredible retro feel, with graphics that are straight out of the NES, and an amazing soundtrack. I haven't finished it yet, but so far the same can be said about both the gameplay and story...it is deceptively simple, oddly brutal, weird and amazing.
It's a top down game where each level basically consists of simply killing all the 'bad guys'. It's ultra violent, and despite the 16 bit style graphics they squeeze quite a lot of detail into various death animations. There are a wide variety of weapons that do all manage to handle a little differently. You can handle combat differently depending on what you have to work with and what your style is, and weapon placement and enemy patrols are somewhat randomized between attempts, which keeps it fresh. You can't simply memorize a whole level.
It's also fairly difficult, but in the fun, rewarding old school Nintendo style difficult. Yell at the screen, toss the controller, immediately pick it up and start again difficult. Not nearly as soul crushing as Super Meat Boy though, so that's kind of a frame of reference.
If you happen to check out reviews some say it was very buggy on release, but at least for me none of that has shown up. They have also added controller support for the 360 controller, which has felt much better for me than the keys.
All in all, amazing game...I already bought two more copies to send to some friends, I really can't recommend it more to anyone who loves old school games, or for any young gameheads willing to try something a little different. Like I said...on sale 50% off thru the weekend on Steam.