Pros
As an International Organization dedicated to Particle Physics research, CERN is a very dynamic place full of enthusiastic people, and the environment is similar to that of a university. This is the perfect place to start a career, full of young people and interesting job offerings not just in the research area, but also in different fields of engineering, IT, computer science, and even administration, finance, and other disciplines focused on the business side.
Cons
The turnover at CERN is higher than in most companies, since one of the main goals of the organization is to be a catalyst to offer training and experience to graduates fresh out of the academic world. There is a lot of knowledge transfer involved so the more senior population spend a fair share of time training newcomers. Another peculiarity of CERN is its career building strategy, which is not really appealing if you want to try and make quick career advances. It's also not guaranteed that one person can stay at the organization for longer than 5-8 years, since this is a hard limit for Staff contracts as per the company's recruitment policies.