Pros
I've worked with SSOE for over 15 years now. Incredible variety of projects offering an opportunity to learn. Strong belief in structured approach to project management. Great culture that allows everyone to hold each other accountable, work through issues, and move forward as a team. Stable employment opportunities for a A/E consulting firm. Multiple divisions in diverse industries, allowing the divisions to "share" employees. If one division gets slow, those employees can often be utilized on projects for another division. They are not quick to layoff in response to downturns, but look for opportunities to put people to work. Despite its size, it's a company that shows loyalty to their individual employees, and offers opportunities and responsibility to those who desire.
Cons
As with any consulting firm, the balance between number of employees and the amount of work is never quite achieved. Either too much work and not enough employees, or too little work for the number of people on staff. It's impossible to hit that perfect balance.