I am a biased Hitman fan having played all the games but I have now played Assassins Creed on both Xbox and PC and love it.
You have to play it on PC for the most spectacular graphics and you need a powerful PC as some of the talking cut scenes do are not in sync with the sound but in terms of the vastness of the game you can tell the developers spent ages on it.
Hitman is about strategy which I love but so is assassins creed if you let it. If you think about how to make an assassination look good then it is all worth it.
I know other reviews complain that the game is linear which it is in terms of missions and collecting information about your target but as you progress through the game you gain new abilities that, if you try to use them, make it more challenging.
Also when it comes to an assassination there are 3 - 4 different ways you could kill them. Even running around the cities killing off guards and templars can be fun. Try hanging off a wall, enter high profile mode and then assassinate and Altair will jump, land and kill.
It is a thing of beauty.
I would stress that you need the Xbox 360 controller for windows to really be able to think quick and change weapons during a battle.
If you cannot find anything good about this game then scale a building and look at the scenary.