Pros
Incredibly knowledgable, professional, and caring teammates -- Each and every person I encountered cared deeply about the American taxpayers, and was devoted to the work they did. At the end of my first month, I had a manager retired after 40 years of service -- that's emblematic of the dedication that the people working at the IRS had. Some of the brightest and most experienced minds in analysis -- I worked as an analyst and had the privilege to interact with over a dozen teams during my tenure. Each and every person was incredibly experienced genuinely cared about me. Additionally, because the agency tends to have staff on board for such long periods of time, most people were very knowledgeable about the IRS and its inner-workings which made learning easy. Big problems that matter -- On my first day, I got asked to quantify a $400 million dollar tax compliance problem. After that project, I was working on developing strategies for a $20 billion dollar revenue stream. When you're working with the country's financial data, every project is absolutely enormous. I loved coming into work each day and tackling issues with scale that truly mattered to the country. Data, Data, Everywhere and all available to analyze -- The IRS is one of the most data-rich environments out there. Some of the documentation, training, and experience here is on par with the world's best and biggest tech companies (if not better). This place is literally a dream for a data wonk. The work I did here set me up and had recruiters knocking on my door every other week. Stable (relatively) Job -- You have incredible job stability. The statistics don't lie... you're more likely to die on the job than get fired.
Cons
Political battleground -- As someone who really loved doing the work and making the agency better, it hurt hearing the way politicians and friends demonize the agency. As long as you get used to being bashed in the news/media -- you're all set! Promotion = Tenure -- No matter how good or hard you worked, promotions were awarded narrowly based on time at level, and number of years spent in the seat. I had some analysts with 20+ years of experience that I was teaching how to do a LEFT JOIN Old School -- Technology in some areas is very advanced (data infrastructure, cataloguing, etc.), but very outdated in others (SAS 2003... shudders). Average/Below-Average Pay -- When I left the IRS I made 2X-3X as much going into private sector. Bureaucracy -- You enter an agency where the bulk of the workforce is set to retire in 10 years. This also means that they hold onto old, mundane hierarchies that boggle the mind. I had some meetings where I was not allowed to sit at the main table since I was a junior analyst.