Pros
An open minded and diverse company with owners that I have always found willing to give the greatest opportunities to those that are bright, client service savvy, passionate about their interests, loyal and committed. It's not for everyone but then who wants to work for a company that's for everyone? The culture of the company is almost anti-corporate, which is great if you're not for the corporate world. It's a lot of fun and very creative, with a ton of constant daily interaction between people in different disciplines because of the way all of the offices are organised. Because of the structure, people can learn a lot very quickly from each other as much outside of their discipline as within. Collision of ideas and creative problem solving seems to happen perpetually which I've seen produce some really innovative and respected client work over the years. The pace is pretty frenetic which is exciting for people that thrive in those kind of environments and there's a genuinely good deal of variety because of the range of types and sizes of clients the company works with. The much sought after consultancy and strategy opportunities are available to pretty much anyone that works on projects and aren't just the domain of special "consultant" people which provides a great career path for people to develop in just about all project level or client facing roles. Hierarchy doesn't really dictate here whether you can comment on others work for the better or improve the output by offering your own ideas, even if what you're commenting on is outside of your discipline. The people that really succeed at this company work very hard, often their lives revolve around their shared interests in the business at hand and for some it's pretty all consuming but not without reward or enjoyment. Most if not all seem to make many friends for life here.
Cons
The company culture is not for everyone. Some [but to be fair not all] people that prefer hierarchy and more traditional methods of management, consultancy or delivery tend to struggle with the pace. The company tends to be exceptionally flexible with people for exceptional circumstances for short periods of time, but the kind of flexible working routinely offered by much larger companies or in the public sector is not yet present here. Benefits - pay is good and pay rises to those that the company wants to be a part of it's growth are certainly part of the reward system, but as yet, other benefits like health insurance or fitness membership that you might get at a larger corporate are missing. The business is growing and to be fair this is now changing.