Vault101 said:
No, Hitman isn't based on the video game, it's set in a Gotham slum and Tommy Monaghan (never called "Hitman" in the comics) is the main character. He is a Gulf War Veteran who decides to become a contract killer specializing in metahumans after he acquires X-Ray vision and mild telepathy. It is set in the established DC Universe and has appearances of Batman, The Joker, Green Lantern, Catwoman and others including a great encounter with Superman.
As to why I'd really only recommend TDKR by Miller and Hitman by Ennis. Well firstly they are each writer's best books/runs IMO.
They are also the most accessible books by these writers. OK Batman: Year One and the Miller Daredevil stuff aren't too hard to get into or confronting, but they also aren't as good as TDKR...and some of Miller's later stuff is just a bit shit. I can find stuff to admire in the art of Sin City but I think by that stage Miller had almost become a parody of himself.
As for Ennis, like I said, Preacher was a bit too angry and that makes it a little unfocused, and I also think Ennis went off the rails a bit post Hitman. Hitman, while pretty violent, isn't too confronting, and it has a classic tragic arc that is a bit missing in Ennis' later stuff. Really though Ennis is best left to people who like Ennis, Hitman gives people a taste of Ennis at his best, while still remaining fairly friendly for everbody...also it has Dogwelder!