'To opt out of the Beta and resume playing the current version of the game, select 'NONE' in the drop down box of the BETAS tab. This will prompt another restart and will require you to re-download the current Public files.'
What is the point of this change?
All I want is:
Ability to open options while in a game lobby.
Ability to view friends after queueing for a game.
Ability to invite random players who are looking for a group. Not just join their lobby but invite them to yours too...
new UI provides a platform for further integration of features, something that the current UI cannot really do, at least not efficiently.
So either way having a new UI only helps, even if you don't care much for the current visible changes.
[The panel-based UI, which has been in the works for over two years now], "enables rapid development, high quality, and high-performance interfaces as well as seamless integration with game content", [according to Valve's development website.]