Pros
I really liked the people I worked with. Most people were competent and hard working while still being friendly and interesting to talk to (that can make all the difference during the long days!). The benefits were pretty good (though I was disappointed when they switched to an inferior health insurance provider just before I left and also with the paltry transit subsidy). I was given excellent opportunities for professional growth, able to work on very interesting and societally relevant projects and was entrusted with a lot of responsibility after just a year (there and out of college). Note though that such things varied widely across practices (I was in the climate group) and managers. All in all, a steady job, decent compensation (though they could do better there) and interesting work. Not somewhere I wanted to stay forever, but it was a good first job experience and prepared me well for my next job.
Cons
Of course, as a consulting firm, billable hours are key. It seemed that to gain recognition you had to work ridiculous hours. The quality of work was a minor factor (if one at all), what really mattered - how many hours you billed. This can be frustrating for competent, efficient workers who value a true work life balance. Also, opportunities for advancement (i.e., promotions) seemed inflexible. Even if you were successfully managing responsibilities far beyond those of your position, if you didn't have x number of years in, you "couldn't" get promoted. Finally, it seemed like the practices were reorganized every six months. This was confusing and did not improve operations (how could it if you were constantly relearning how things were supposed to work).