Pros
You will learn a lot very fast, massive exposure in little time. I would not be where I am today without the experience. You will learn more in a year than some will learn in 5 at an in house IT team. The team was great and always helpful. That being said, you have to adapt to a huge number of softwares and networks very quickly. There have been great strides in documentation. When you are good at something, it is noticed and appreciated. Free snacks and lunch provided on Fridays. Required certifications are paid for.
Cons
There was a lot of turnover. Pay raises were always "if you bring x things to the table in x time, you'll get it" make sure your salary is gonna make you happy for a few years. Weekends on call are required with no compensation. Vacation and holidays are sparse and you can get called on those.