When I was little, I'd read the hell out of any manual that came with my games. Most of them had backstory, character bios, pictures, ect.
Not to mention they smell nice.
...
Don't look at me like that, I'm not crazy I swear.
Now-a-days though, manuals just seem to be an afterthought. Not much is put into them. Hell, Arkham City's manual is practically nothing but advertisement for Batman related merchandise.