Vantaggi
Collaborative decision making, extremely broad range of issues to research and gain expertise on (you won't get assigned to working foreign tax credit issues for a year, like happens at Big 4), fairly flat work organization. I disagree with many other posters that pay raises are based on seniority alone - I have had several merit increases and get other bonuses in years when I am prevented from receiving a merit (permanent) salary increase.
Svantaggi
Aging workforce and management. Incredibly techno-phobic workplace. The IRS solution to Information Tech is to block it, prevent it, ignore it, all while saying they need to do this to maintain taxpayer confidence. This issue comes up regularly at mtgs with taxpayers, who shake their head in amazement at how backward the IRS systems are.