Pros
PromptWorks is the best place I've ever worked because they "get it." They promote good software design, pair programming, Agile principles, and test-driven development. Other places I've worked talk about Agile but don't really do it and I think pairing is the key. We keep each other accountable for writing a test before we write code, for example. Now that I'm pairing most every day, it would be hard to go back to sitting in front of a computer by myself all day long—it's too easy to go down rabbit holes and waste time! Work-life balance is great. I have work time set aside to do my open source work and side projects. Their office is super close to public transportation and the lunch options around are pretty good. They buy us lunch twice a week and we talk about the company, discuss programming books, or play games. I feel like I have friends at work and the founders are really accessible, which is good because they have so much experience consulting and writing software.
Kontras
They're a small and fairly young company. Things change a lot, like we're now changing pairing partners daily instead of weekly, but changes are usually discussed in the group. Some changes are good, like adding benefits. There's not always clear direction from the founders, so sometimes you have to figure things out for yourself and different people will take different approaches.