Pros
The Park Service can be fun to work for and can be good to put on a resume. If you stick with it long enough, it can provide good government retirement benefits.
Cons
For me, the cons definitely outweigh the pros. It can be very difficult to get your foot in the door even as a seasonal let alone as a permanent. To move up in GS levels, you have to move parks often, making it hard to lay down roots or build friendships. Pay isn't great either, which, in combination with having to move often, makes having a family difficult if that is on your radar. In general, there seems to be a culture of apathy that used not to exist in the Park Service, and I truly hope that can be corrected. I think some of the cons I experienced were specific to my park, but the red tape and outdated government policies are persistent throughout many parks.