Pros
The Library offers a dizzying amount of classes and training, if you are ambitious. Some are mandatory, but most are not. If you're smart, you'll avail every opportunity. Most staff, though by far not all, are courtesy and professional, and very easy to get along with. You'll make many long-lasting friendships. The Library encourages staff to develop innovative programs for the public, and are quite supportive of staff efforts.
Cons
Since it is union (which can be a very good thing!), unfortunately bad apples are almost impossible to get rid of. There are plenty of people who don't pull their weight, and do nothing with attitude. The chance for advancement is scarce; many professional positions now do not require MLSs, thus taking away jobs once held my librarians. All about the all mighty dollar. Management in the upper eschelon are business people, most with no experience in non-profits. And it shows. Many changes have been made over the years that most staff find deleterious to the mission of the library. For example, monetizing libraries (i.e., selling off library properties to developers), thus shrinking the system of needed, very busy libraries.