Pros
Great environment. Highly skilled IT professionals. Fair and open management. Good compensation. Opportunity to learn new technologies. Nobody gets laid off even during recession. Overall it's much better than an average consulting experience, but could be somewhat worse than a good full-time work.
Cons
The company is centered around handful of bigger clients. It results in a lack of interesting project opportunities and potential instability. Absolutely no career growth opportunity as all people are essentially consultants, who simply do what client requires on a project. While compensation is above average, its growth is way below average. Management rarely pushes back when it comes to unreasonable client requirements putting all the burden on consultants. Not enough interaction between company employees due to rare gatherings.