I really, really enjoyed The Darkness, even though it didn't have the best gameplay mechanics. It did something very different, had a GREAT story, brilliant art direction, and superb voice acting. The Darkness powers were pretty damn cool too. It was one of those games that you really got attached to.
Alas, I rented it and beat it in about 7 hours. I really need to pick it up again, it was a load of fun while it lasted