It doesn't help that it was rolled out as the default well before simple existing features like "rankings other than 'hot' on user pages" were implemented.
But destroying old CSS and then not displaying sidebar text in the new default view is what's going to have serious consequences. For all the talk about customization and moderator tools, they've made it so that new users won't see sidebars of rules, useful links, or related subs. Talk about undermining engagement and useful contributions...
The whole pattern of ads that 'scale down' as you scroll is horrid. It's a jarring event, usually doesn't happen smoothly as intended, and it almost always heralds an object that's going to follow you down the page. Nothing except maybe tactful menu bars should follow a user scrolling down a page of static text.