I was a bit surprised, but I quite like the new look. However, and I hate to be a downer on something you've obviously put a lot of work in to, my first view of it was the community page not looking right:
Every other page is lined up fine though. I'm using Firefox 3.6.13.
And I really miss the multiple screenshot thumbnails too, I often look at an addon, scan the thumbnails and pick the screenshot of most interest to open up, to have to open up the lightbox, wait for it to load, click through and wait for the picture I want to load is a bit meh.
The icons for the addon categories are great though! And I like the drop down navigation (though when you mouseover Forums and click Categories (rather than click on the actual categories on the sub menu) you get taken to the addons categories page rather than
http://www.wowinterface.com/forums/index.php..)