Pros
The design team is incredibly talented and some of the projects turn into key portfolio pieces that will likely get published and win awards. You'll also become close with your fellow coworkers because you're all under extreme conditions that breed comradery. The environment will also make you tough. One year will teach you volumes about yourself and how to deal with high levels of pressure. The best skill you will learn is how to borrow inspiration and take it to a new place.
Cons
There is zero project management. Project timelines are arbitrary and will change at the owners whim. Be prepared for random internal meetings after 6:00pm and routine late nights. The average work day is 9:30am - 8:00pm and no one will thank you for working past 8, it's generally expected. The tension in the air palpable, mostly because the owners arguments are loud and frequent. Design briefs are verbal, very limited in helpful information and generally a loose interpretation of what clients really asked for. They have no idea what strategy really takes or how to implement it. Every projects direction is edgy, fashion, and not American in aesthetic.