Pros
The general public believes that all attorneys at the IRS do Tax work, yet there are opportunities for just about every type of government administrative law practice at the IRS Office of Chief Counsel. Unlike most federal agencies who rely upon the Department of Justice tor all their trial work, IRS attorneys actually represent the IRS directly in Bankruptcy court, as Special US Attorneys. Moreover, the General Legal Services Division of IRS handles Ethics, Contracts, Labor Law, Approriations law etc. It was the IRS Office of Chief Counsel that successfully resisted a combined government and industry attempt to force taxpayers to use a cumbersome and expensive Public Key Infrastructure electronic signature for tax returns instead of a consume friendly PIN. Of course, if you do want to do tax work, then the IRS is the place for you since you will get more authority and experience in your first five years than at any private tax practice.
Cons
The IRS is the quintessential bureaucracy so you have to have a high tolerance for silly rules. The worst part of being an IRS employee is the general public's antipathy towards you. Nothing has changed since Biblical times when the tax collector was reviled. IRS employees learn early to tell strangers that they work for Treasury