Avantages
You'll be working with systems that function on a scale that very, very few other companies have to worry about. Every year, they have to push the envelope to survive the Christmas season without melting down. It's something that you don't get elsewhere.
Inconvénients
On call and operation load is a significant part of the job, but not a significant part of the job description. There is little effort to retain or reward employees. Employees are given responsibility over projects, but not the authority to make changes. It's a very top down company, and sadly, there are often cases where a project is redesigned at the last minute because middle management didn't get sign off from senior management, or senior management was flakey. There's no institutional memory, because of the high turnover. This means that people are reinventing the wheel a lot, often in parallel.