Pros
Good atmosphere - management had a lot of faith in employees to work within their area of expertise (like zero micromanaging), and for most people it worked really well. Definitely a good fit for people who are self motivated (and not a great fit for those who aren't). People are generally motivated to work hard, but not past a work-life balance. People there, including management, are kind and easy to get along with. The CEO is very thoughtful and makes a real effort to get to know everyone - and he's especially respectful of each individual's area of expertise.
Cons
Wasn't a huge fan of the open-office environment, although it helped to have a lot of meeting rooms available - for meetings and sometimes just a quiet place to work. Now that they've joined forces with a larger company, there is some level of 'bureaucracy', although I'd stress that's a real minor issue.