Have been using this new theme since beta. I love the much cleaner look more than the previous one. One can always tune the CSS yourself at the user's preference near the theme selector. The only thing I need to adjust to my liking is to limit the line width:

    main#content {
      max-width: 40em;
    }

For those who hate it: you will always have the option to switch back to the old theme.

I really hope any website could be as flexible as Wikipedia to allow users to write their own CSS.