Vantaggi
You do feel like you make a difference in the lives of taxpayers and U.S. citizens, by processing their returns and getting their refunds back to them on time. And if you are converted to permanent, then the federal benefits can be a great upside. Plenty of positions to get hired for, like accounting and engineering.
Svantaggi
Job with government at any level is full of red tape, inefficiency and waste. There are so many complicated rules and procedures that employees are forced to remember, and these get revised about every year (sometimes they even conflict with one another). Salaries are considerably less than in the private sector and so there's a LOT of turnover at both the managerial and employee level. Expect to work for the government at least 5-10 years before getting to enjoy any actual benefits (you'll be seasonal).