Aside from fare class, the old UI just works better and is faster.

With the new search, if I could depart on, say, Sunday night or Monday morning, trying to change the departure date frequently causes the entire size to freeze or error out. The fancy animated panes get in the way of each other, and just typing a 3-character airport code doesn't work unless you also switch to your mouse and click on the code you just typed. It's miserable.