Pros
Quite simply, your work is in places that others go to vacation. Job security is pretty strong as its a government job. Health benefits and retirement benefits are average, but not as great as people may think. Salary is hit or miss based on where you live. Low cost of living areas, Fed salaries oftentimes are great compared to similar jobs in private sector. High cost of living areas, you will scrape by as cost of living salary adjustments are ridiculously undervalued for these high cost areas.
Cons
As a government bureaucracy, competency and efficiency are not a part of the work culture. Salaries oftentimes do not match the responsibilities. Very little effective communication occurs although its severity is affected at a local level as there are over 360+ parks not including support offices, DC headquarters, and regional offices. Very little uniformity in operations as much of the NPS is decentralized. What is a fun place to work in place, could not be so much in an another. Hiring is inefficient and localized to a certain extent. Your mileage regarding training, career development, leadership, respect, and feedback may vary depending where you work and who you work for in this agency. You will work with some dedicated people as well as some people who you wonder why they even applied for the job. This job can have as much stress, angst, and frustration as any other job out there. Don't be fooled into thinking its all about going hiking for a living.