Steam's official launch of the new library has arrived and it's not nearly as well-received as Valve would probably like. The new library UI lacks older features like proper library sorting and the new image-heavy UI is probably what makes it much slower.
Steam's old library was a neat list of games for the users. It was snappy and in case they were sharing libraries with a friend or family, each library had its own section that could be collapsed or expanded when necessary. Furthermore, any free to play games that a user may have enjoyed in the past but deleted later on, were not showing in the library, which prevented clogging.
All of these features are gone with the new, fancy library. Granted, it looks pretty due to all the images and the home page which acts like a hub for all the news related to the currently installed games, but that's pretty much it.
Users can also create their own custom collections of games, where they can import portions of their library, based on predefined tags, such as "Singleplayer", "RPG", "Adventure" and more.
Normally, this is a great addition that helps with the sorting but it's overshadowed by the regular library's clogged UI that stuffs all the games you came in touch with into a single list. Some of those games are not even around anymore. For example, Tactical Intervention could be added to one's library, despite the game being defunct for years now.