Firstly, there is no search bar at the bottom of the page any more. You can’t refine your search after deciding that the first page of results wasn’t good.
Secondly, it’s buggy. Enter key does not reliably perform a search. You can’t reliably go back to get a previous “instant page” of results.
Thirdly, it doesn’t interact well with browsers. Safari at least always gives you the dialog about how “you’ve typed something, do you really want to close the window”.
Worst of all you don’t seem to be able to permanently disable it and go back to the old style.