Pros
It's a firm that's big enough so you can learn a lot about either auditing or tax, but no so big that you're just a number. I would say that in comparison to the "big 4" accounting firms, people generally have a slightly lighter workload, which is nice. In addition, each office does fun things for its employees like sponsoring sporting leagues or paying for happy hours.
Cons
Like with any public accounting firm, work hours can be long when busy season hits. RSM suffers from some of the same problems that plague public accounting in general: a grueling work schedule, an uptight corporate culture, and a problem with work/life balance. I think maybe RSM is a little better at some of these issues than other CPA firms but it still has a long way to go.