The games library is terrible. It shows all of your games in a horizontal list that just shows boxarts that is kind of similar to the friends list on the NXE dashboard. It doesn't let you auto-scroll back to the top when you reach the bottom either, so it's kind of clunky when the old text list was good as is. I'd have loved to have customization options to organize my games library how I please like the PS3's folder system since I don't like having XBLA demos mixed in with paid games.
The good thing about the games library is that clicking on a game brings up a page that's similar to the Games Marketplace page for that game with the themed background, ways to access the DLC and such on the marketplace page, and leaderboards/achievements that makes it a huge upgrade over the bland pages that had just had achievements/leaderboards.
For people wondering, the cloud storage gives you 511 MB to work with. I don't think I see an option to tell it to automatically upload saves for certain games to the cloud
If you liked the custom backgrounds for the NXE friends list, they kind of appear when you click on yourself under the social tab. NXE themes still work, but there's nothing in the bottom half of the screen since NXE blocked that part of the themes.