Vantaggi
People, experience, some of the benefits package. You work with other people like yourself, and you work at major clients. It can be challenging and fun at the same time. There are always opportunities to make working a more valuable learning experience, while also working with smart individuals who generally like to have fun. The assortment of clients and work demand can also take you to different cities (and many times different countries), which can be exciting opportunities for those interested in that sort of thing. Additionally, starting a job there with 25 days of PTO is very compelling for those who like to use it.
Svantaggi
Performance evaluation always forced awkward ratings and the perception (and sometimes reality) of unfair assessments. Work/Life balance was an afterthought at some clients. Project situations will always differ from client to client, but I feel like this could be managed better to keep people from working very many weekends.