This is by far my favourite game in the Hitman series. The missions are great, with memorable settings, many different routes and an incredible number of very reasonable, intuitive solutions to get your kills. Couple that with state of art level design, and you have the perfect Hitman game: more accessible than hitman 2 and not plagued by silly checkpoints like Absolution. You can set your own pace and figure out all that happens around you; concoct your plan and proceed to the assassination. Then savor that sweet, sweet kill-cam before walking away unnoticed like a real boss.
The story is very loose, but a truly epic ending ties it all together nicely.
If you are new to the series or want to give old 47 another shot, just pick this game and let it do its thing. It doesn't get any better.