Pros
1. The people - your co-workers are really the best part about OW. Everyone is interesting and talented, and that makes the long hours worthwhile. 2. You learn a lot. Whether you want to jump around between industries or dive into one area of interest, you are fully immersed and you work on a lot of skills. 3. Ability to progress in the company - OW is a meritocratic environment. You can progress to whatever level you are performing at. Additionally, OW does not have an MBA hiring track, and thus invests more time and effort on their undergraduate hires.
Cons
1. Lifestyle - you travel a lot, and you work late hours. This isn't really different among top management consulting companies, but be aware of it going in. 2. Element of chance in staffing - a lot of your experience depends on what cases you get onto. And while you can express preferences for staffing, your cases can depend a lot on the chance of timing (when you become free, when other cases are starting). Also, one bad case with a manager that you really don't get along with can be both a miserable experience and set you back significantly in career progression.