Pros
8 years here, haven't had a boring day at work yet. Every day brings new challenges and obstacles to figure out, and at the end of the day you wonder where the hours have gone. Opportunities to pursue your interests and expand your scope of knowledge at work are nearly endless, and you'll be learning some of the most motivated and phenomenally smart people on earth. You can write your own story here, so long as you excel at it. Here, you can go as far as you are capable, and the satisfaction from contributing to the highest-aiming goals around is unparalleled.
Cons
Relentless pressure and schedule. Everyone has double to triple the workload that could ever be achieved, and the target is always moving. This proves troublesome to people used to organization and regular schedules. It can be disruptive to life outside of work, since 50+ hour weeks and months of travel can take their toll. If you're not a self-motivator or struggle with time management and organization, you will sink. This is not a place for those who need babysitters or the faint of heart.