Pros
I've never learned more in a shorter period of time ever in my career. Junior staff are highly motivated and supportive, I loved my coworkers. High expectations for client deliverables. I've heard from other BRG friends that other offices are better. It all depends on your manager. It made me a better analyst, motivated me to go to graduate school.
Cons
If you end up with a bad manager (as I did) you are in hell. Ended up working for an expert who all the other junior staffers refused to work with. I quit after seven months because HR listened to none of my complaints. HR is essentially non-existent. My office was definitely and old boys club, if you are a smart white male in management you can treat your junior staff however you want and rarely will it have consequences. Head of my office made disparaging comments about a woman on maternity leave.