Pros
Perks of being attached to a large public university: use of campus buildings and facilities, library access, winter break closure, tuition remission, retirement, etc. LOVED the atmosphere of working on a college campus and with students. GMU has a large commuter population, so you get a varied group of students and frequently those that are dedicated and juggling life commitments along with school. Less entitled Greek life shenanigans, etc.
Cons
Have to pay for parking Low salaries: GMU uses Virginia state's pay banding. Staff are hired in at the bottom of their pay band with little to no room for negotiation. Even after leaving GMU, I have acquaintances who turned down job offers due to the lack of negotiation. Raises are so little that I (and my colleagues with < 10 years experience) would sometime get a "raise" when the pay band moved up slightly and we fell off the bottom of it. It isn't great for morale to keep employees permanently at the bottom of the band. Every other year, the governor authorizes a one-time bonus instead of a raise. Which means that your base comp doesn't go up for next year, and you are in the same position again. High performers aren't recognized for their work. Promotions and raises are hard to achieve due to the built-in bureaucracy. Even though the university is large, there frequently isn't a place for you to move up and no other incentives to provide to make up for it.