I've been able to put up with it, but there are so many forced-changes in there it makes me wonder if even at Valve there's a steam-faced portion of the staff angry about the change.
The UI fails to provide distinctions in color between different sections; it's all this dark black color. It sucks up far more memory than it should for a BACKGROUND PROGRAM for RUNNING MEMORY-INTENSIVE PROGRAMS. Many people, such as the OP, had issues involving needing to reinstall their whole games list (the advice to "reinstall the DLLs" is not helpful if someone has to go on a forum and wait several days for a reply to get it. How about saying it in the error message?) The new view list indiscriminately lists your Uninstalled games with your Installed, and the only way to fix it is to COMPLETELY hide the Uninstalled games, meaning you have to switch view twice if you ever want to install something.
I could go on, but I can't afford to break three keyboards listing everything wrong with it. At the very LEAST they could support the previous version for SOME time as people adjust over. Imagine if Microsoft suddenly said "EVERYONE MUST NOW USE WINDOWS 7". Don't get me wrong, 7 is awesome, but that would be a bad move.