Pros
I've never worked with anyone at Slalom and thought to myself, I never want to work with that person again - Slalom attracts good people. I can't say the same for past consulting firms and agencies I've worked for. I also believe that my leadership is some of the best that I've ever worked for and I am constantly challenged by the people around me.
Cons
Consulting is consulting - if you don't like, Slalom isn't going to change that for you. You're going to have tough clients, there's going to be politics, and you're going to have to work long hours sometimes. Personally, I don't think this is a con - I chose consulting, but I think some people come to Slalom thinking that it's going to be different, and while culturally it is, the work is still the same, and clients are still the same. This becomes a con when people's expectations are met, so set your expectations accordingly.