Pros
It gives one an opportunity to network with some of the brightest people in the industry. The company is large, so there are also good clients that one can work on. Another advantage of its size is the number of offices that KPMG has, so one can try to internally transfer anywhere in the world. The benefits are also good, such as 25 days off, generous 401k matching contributions, and decent salary. Many of the partners are also very relaxed and calm. I would say most of the managers are as well, but there are some that tend to be uptight.
Cons
It is easy to be pigeon holed into an industry. It mostly depends on which service line that one joins, as well as the location of the office that he/she joins. For example, in the NE offices, employees work mostly on financial firms, in SF and SV, the clients are mostly technology related, and in the SW, it is mostly energy. If one doesn't like the industries that his/her office specializes in, it can be difficult to enjoy ones work. Also, because it is such a big company, there are some less than smart people that are able to squeeze through the cracks and gain employement.