Pros
Good pay, benefits, and time off. You get to spend lots of time outside of the office working cases. You get to see many different businesses. On Monday you may be at a doctor's office and on Thursday at a gas station. Managers are pretty predictable. Once you learn the things that they harp on it is easy to stay under the radar and get the job done.
Cons
The organization is completely disorganized. Looking up procedures or other information on the the IRS intranet yields out of date and contradictory information. Looking up items in the manual (our rule book the IRM) can also do the same. Furthermore, no one in the company ever wants to make definite statements. So even when dealing with a so-called authority on a subject you can't get any answers. Annual reviews are what a person relies on to get promotions within the government. Employees in an office that seem to do nothing else than socialize all day get awards. While those that seem to be working do not. I have even had my boss tell me that she could not give me the review I earned because upper management does not like it when reviews increase too fast so she has to rate me lower than I am actually preforming at. No one seems to know what they are doing. You find a few gems in the company but by and large if something unusual comes up you have to look it up and just do what you think is right. Later when your manager comes down on you for taking some initiative you just have to sit there and take it. The IRS has a union contract that provides specific benefits such as paying for the CPA review course, alternative work schedules, etc. However, IRS does not honor it. So if you want to take advantage of some of the benefits you have to put in a formal claim with the union for it.