Pros
You get paid well and it really helps to advance your career and job opportunities if you work for any of the Big 4 accounting firms. Starting out as a new hire associate you get 5 weeks of vacation a year which is more than most people get after 10 years with the same company. Health care benefits are really good with a variety of plans to choose from. I have never had time off requested denied. KPMG really understand worklife balance.
Kontras
I think there may be more downsides if you are in Audit or Tax rather than advisory. Audit and Tax really seem to have long hard busy seasons sometimes working 80 hours a week. However, in advisory we normally have a busy season for only about a month where we work 50 hrs a week. Something else that could be a downside is that we are always at a client site. One week your commute might just be 15 minutes but another week you could be staffed on a different client and your commute is now an hour.