Pros
Work-life balance is great, if you know what you're doing there is never an excuse to stay past 6pm. Benefits are very fair. For the most part everyone there's a good person.
Cons
Agree with most of the above negative comments. Probably an ok place to start right out of college, but past a certain point you're going to have to leave if you want any kind of career development. Poor management of expectations sometimes masquerades as "entrepreneurial," so you'd better be sure you have a realistic idea what you're going to achieve. Flat structure often confuses who is responsible when something goes wrong, which happens far too often given the firm's AUM. I was always amazed how out of touch managers, directors, and partners could be, especially since they normally sit a cubicle or two away.