Just to add, the game does have a digital manual in the main menu section, which is surprisingly decent given the current nature of manuals in general. It covers everything briefly enough so that you know all you need to.
According to the GameTrailers review, the campaign is the shortest of the series at around 6 hours. But they said still gave the game a 9 saying the short campaign isn't a big deal b/c it's a very good campaign with lots of variety. I don't like Crysis so all I can say objectively is what I've heard from other places.