Pros
CNN offers a tremendous amount of resources at the hands of every professional working within its walls. Each individual carries a strength to the production team that makes it one of the most intellectually stimulating environments. Senior colleagues have a breadth of expertise in fields that they have covered issues an entire career over. As junior staff they place an incredible amount of trust in your abilities that ultimately allow you to build on your portfolio. Each day offered new and exciting opportunities and that certainly beat working the traditional and predictable 9-6 M-F job where your work followed you each day of the week. You must be willing to "give it your all."
Cons
You must have the ability to balance your personal life. If building your career is a priority over maintaining your social and personal life then this is the perfect match. If your social life is of the utmost importance, then CNN along with the entire broadcast news industry certainly is not for you.