Pros
NYPL is a huge & well-known institution with an excellent reputation. The library is making a significant and largely effective effort to grow with the times and remain relevant. Municipal benefits package is very good as are tuition benefits. The trainee program is an excellent way to learn on the job while getting your MLS - progressive promotions are given as you earn more credits. It's a very good jump-off point for the budding librarian.
Cons
Public service can be very demanding and sometimes demoralizing. Burnout is a widespread condition. Government funding sometimes means scrimping and saving to provide necessary services and programs for patrons. On a related note, salary at a public library is very low compared to private or academic libraries. It's a great job to start out in, but once you've got the experience & the entry on your resume, it might be time to move on.