Pros
The people I worked with genuinely care about both their staff and client relationships. Partners & managers are always helping out staff & getting them involved with the clients. They are very flexible and work with you if you have specific schedule needs -- they also offer a good amount of paid time off. When I expressed an interest in doing other things I was always given the opportunity. If you approach people with good ideas, they do listen. There was open communication across the board. The environment is professional but informal. Long tax season hours are unavoidable, but they try their best to make it less painful -- there's a lot of free food and they've tried things like giving folks a Saturday off. They're also pretty lenient at other times of the year to make up for it.
Cons
Everyone is so busy that there's little time or energy left to focus on making things better. Committees are thrown together but go nowhere. It was much nicer as a small firm but has become very process-heavy and bureaucratic in the last few years. Also, the Bethesda office is a sea of gray cubicles; very drab & sterile looking (though I hear other offices are quite nice). In the administrative/executive assistant role, there aren't many opportunities for advancement (but I think that's to be expected as there are far fewer higher-level administrative positions and the promotion ladder is focused on the CPAs). Exceptionally performing admins have gone on to do other things, but that's not the norm. There is definitely the attitude that an admin's time is not as valuable because it's all about billable time, so as bad as they are figuring out more efficient ways of doing billable work, they're even worse alleviating admin work, because it just isn't a priority.