Pros
I get to work with really smart, passionate people. There's a ton of variety in the work that we do, and that keeps things interesting. There's a good amount of autonomy and flexibility granted to consultants. We're treated like adults who can make decisions for themselves. There's a lot of room for creativity and innovative thinking, if you get on the right projects. The energy practice (where I work) has a good blend of thinkers from different fields: engineers, economists, B-school grads, social scientists, etc. I feel very proud of our reputation for quality in our field.
Cons
I am acutely aware that many people have had a less positive experience than I have; so much depends on which office you're in and which project managers you're working with. Some of the offices have no camaraderie (thankfully, I am in one of the ones with a good culture). Some project managers treat their employees like indentured servants but many are excellent and nurturing. Performance evaluations focus too much on how much time you bill to the client and not enough on how much value you create for the client and what you do to ensure the long-term success of your group. There's a lot of talk about building a "sales culture" but at the lower levels, there is really no upside to spending non-billable time on trying to sell work. I think there's a lot of short-sightedness in the performance evaluation process. There could be more collaboration across teams and groups. A good amount of reinventing the wheel takes place. That's partially due to the emphasis on billable hours. Nobody wants to spend a ton of time that they don't get credit for making things easier for other people.