Pros
Great Benefits. Learn a lot. Good atmosphere for the most part with select people. Depending on your position, you might be able to travel for work, or even go out of the country for 1-2 years.
Cons
Too much competition. These are young and smart minds that feel a lot of entitlement to everything. Long hours with little pay. Expect to work 50-60 hrs a week for entry level. You have to leave and come back to make more money here. Principles make anywhere up to $450K a year, these are people that came from the outside. Depending on who your supervisor is, you might like or dislike coming into work. If you are applying for Facilities, IT, Media team, you are everyone else's work horse. The Americas organization of Arup is always strapped for cash, so don't expect a big pay raise.