Even if you aren't a fan of the comics, I would still recommend giving this game a try. The Darkness powers are fun to use (especially Creeping Dark, which is a snake thing that you can use to remotely attack your enemies), even if the gunplay is pretty vanilla. The game begins with an awesome car chase that ends specatacularly. Needless to say you then proceed to shoot a bunch of people. Not long after, you gain the powers of the Darkness, and you can let your inner demon out. Killing people in various and brutal manners is pretty darn fun.
But what drew me to this game the most was the rich story and believable charaters. In fact, I believe the story outshines the gameplay. Being a fan of the comics I do find some of the liberties taken with some of the mythology a little odd, but that's just nitpicking. The only knock I feel I have on this game overall is that you spend way too much time in the subway station in between missions, and traversing long distances through an almost empty New York can be a little strange. But overall it's a great game that has sadly been overlooked.