You can download a demo of it. If you loved the original, you might not like The Darkness 2 as much. It's a lot more linear and mainstream. They altered the style of play to appeal to more gamers. The first was kind of a cult hit, and I loved the openness of the game, and the ability to play at your own pace. It also had more thinking elements to it.
The Darkness 2 is much more fast-paced with more carnage. It depends on what style you prefer. If you like non-stop rip em to shreds action you'll probably love the game. If you want a more conservative experience that is more story-driven, then you might like not like 2 as much.