I saw "Inferno" this afternoon, and much was as I expected, until the end where it diverged 180 degrees from the book. The ending of the book was, IMO, the whole reason for the book to have been written. Since most people have neither read the book nor seen the movie at this point, I have to use a major spoiler.
Do NOT open the spoiler unless you want the cliffhanger plotline spoiled:
The book ends with the plague already having been released; the effects of the plague being a sterilization of a large percentage of the population, bringing future populations down to a sustainable level without actively killing people in war, famine, natural disaster, or hemorrhagic plague. Obviously, such an ending is controversial and designed to encourage bringing the issue of excess population to the consciousness of the general public. By having the movie end with the plague contained, it plays to the sanguine head-in-the-sand response and doesn't offend the religious, thus insuring some money at the box office and little hate mail. It is the type of cop-out that Hollywood has acceded to repeatedly over the years.
The book is longish, but I would choose it over the movie.