Pros
I've been working here for 10 years now and really appreciate the different opportunities I had. I recommend Thoughtworks to anyone looking for opportunities to learn different things (sometimes outside of your comfort zone) in a supportive environment with great people. The work/life balance is amazing, I've worked with people that respect personal boundaries and appreciate everyone's time and effort. Work is planned in a sustainable way and I've almost never worked overtime or on non-working days. If you are someone who wants to push yourself and take every opportunity available you can do that (and you'll find other people with similar interests), and if you're someone who wants to get the job done while still having a healthy life outside of work it also won't be a problem. Another great benefit of working on a global company is being able to travel and work with people from different backgrounds. In the 10 years I've been here I was able to work on 3 different countries and interact with pretty much all offices we have around the globe, so if that's the kind of experience you're looking for Thoughtworks will be a great opportunity for you.
Cons
The loose environment with lack of structure might make it hard for people to understand expectations and growth path, it really depends a lot on the individual to take ownership over their career. While you can learn a lot from the different projects you work on, sometimes you need to work on areas that are not really your expertise or not be something that you necessarily would like to work on.