Pros
The library really has some great services, and they are doing a lot of the city. Overall they have a great mission and great vision. The benefits are decent, and because it's a city job you get other benefits with that. It is definitely a great experience to have - working in a huge urban library system. And having "New York Public Library" on your resume will deinifely open other doors for you! There is room for advancement, because it is a hugh system, but you have to stay in your positio for 12 months before you can transfer to anything else.
Cons
The library system is a little too big to be properly and evenly managed. Some of it is government funded, but a big portion of the funding is private, and so branches in nicer areas of the city get big donations from their patrons, while branches in areas where the community is not as wealthy get nothing. And so the already nice branches get nicer while the branches that are really in need tend to suffer and get swept under the rug. Staffing is also an issue, in the sense that there is never enough. I found that it all also depends which branch you're placed in. The attitude of your manager really effects the whole staff. I have been to other branches where the manager really cares and loves the library, and it is very obvious that the staff at that branch appreciate are happier and want to work hard to make it a nice place because the manager is working hard. Sadly, that's not the case everywhere. Upper management is trying to make some changes for the better, and that is definitely in the works. But people who have been in the system for a long time, and just don't care anymore, can be a bit resistent to change.