Pros
ThoughtWorks tries it best to treat everyone well. The health and wellbeing of its people is a top priority, and that's reflected in the hiring of managers and leaders of people that ascribe to 'servant leadership'. I was (and am) among those. There are also ample career growth opportunities if you are not entirely passive about your career. The tools, people, and client staffing opportunities made available to everyone support a wide variety of career paths.
Cons
You must be at least somewhat of a self-driven, self-directed person to succeed here. A large percentage of the unhappy people I have seen leave the company were not prepared to drive their own career path and take advantage of the opportunities presented to them. Most people - especially in Professional Services doing direct client work - have no solid line boss. You have no-one telling you what to do day-to-day and you can go a long time doing very little and suffering no consequences, leaving you feeling like there is no objective or rhyme or reason. This management format does not work well for some people. With that said, you do have several people senior to you who will guide and mentor you. And, you will have someone on your client engagement that is somewhat responsible for your results. They are the closest person you will have to an official boss. If you come to ThoughtWorks, please be prepared to take charge of your career path.