Welcome to CFC, Sims. The Great Library's hindrance is in giving you techs you dont need at times you dont want them. Every time you get a tech, the number of beakers you need to have for the next one goes up (unless you know the trick of gifting your KeyCiv, if you've made contact with them and are not at war, but even so that cannot bring you down below the increasing base level). If you have a specific tech plan for your start (I usually start with Monarchy/Trade/Philosophy) each extra tech makes the next one take longer. True, working on techs the AI neglect will make the GL pay off better, but if you are not choosing your opponents wisely it is hard to guess what they are shooting for. Marco Polo helps in this area immensely, such that I prioritize it early and leave GL for the AI to waste their time building (I like to get Lit early and hand it off to everyone else; it often causes them to switch from a Wonder I want like Colossus or Copernicus). After it is obsolete (Electricity, which I make a priority getting in mid-game) I'll capture it for the score bonus.