Glory
While there are a lot of hassles that come with the job, it also comes packin' glory. Maybe you're the ranger who finds little Bobby Newton who's been lost in woods for a week. That's got to be satisfying (unless Bobby Newton turns out to be a real jerk who would've done the world a favor by staying in the woods).
There are smaller glories as well. Teaching kids and adults to really appreciate nature for the first time has got to be a personally fulfilling thing. National parks can have a profound effect on people, and being one of the rangers who opens the door to this natural wonderland can have a profound affect on the rangers themselves.