Pros
Shell has a lot of opportunities to move your career in any direction you want, but you have to make your own contacts and plan ahead to move in to another position. As I Was getting my bachelors degree in another field of study than what I was employed in, I Was told I would need to quit Shell and work elsewhere after I got my degree. I remained at Shell for another 16 years after receiving my Bachelors in MIS but I had to acquire interviews as a new college hire through my university (I was already a 13 yr employee at Shell by then) - unconventional method but it worked.
Cons
Not a lot of cons even for a large multi-national petroleum company with 93,000 employees worldwide. As Shell is a foreign owned company, a lot of the preference goes to employees already oversees, or that work oversees frequently and build the familiarity with the decision makers in UK & Netherlands