Pros
Bain offers numerous opportunities for personal and professional growth that are hard to find at other companies, even other consulting firms. The people their are great, I made so many life long friends during my time there -- smart, confident and driven yet enjoy life and don't take themselves too seriously. Finally, Bain is remarkably well-run for such a large oranization. They do a good job of keeping career development and promotions transparent and making sure the staff gets the training and feedback they need to grow and develop.
Cons
It's consulting firm. Bain is a world-class organization and without a doubt the best company I've ever worked for, but if you want to be something other than an adviser, eventually you have to move on.