Pros
Really awesome location to work. Got to work for JPL and be on the campus that made many satellites, and other rovers. Opportunities to work on cool missions and cool projects. Occasionally you get to meet really awesome people who are great to work with. Got to learn about a lot of different things because you are immersed in the workplace. If you open up your mind you can learn a lot. Ability to go to talks on JPL's campus to learn from them and to be inspired. Overall mostly nice people to work with.
Cons
You're a contractor to JPL. You'll always be seen as a secondary and unimportant, and essentially the scapegoat for JPL's problems. Everything is all about the contract and is politicized. Fingerpointing everywhere and no one takes responsibility. HR makes empty promises and makes excuses as to why things cannot be done. Also does not answer questions completely and accurately. Raises/Pay are extremely poor with benefits that aren't great either. Health insurance and retirement are a joke. Mix of old and new technology.