I think one of the biggest things I see is the ability to handle uploads/handling of images inline of your content. You still have to provide the server side implementation (see http://paltman.com/2012/08/15/how-to-setup-upload-handler-fo...) but having the ability to browse previously uploaded photos, as well as upload new ones, and have them appear inline with your content with resize handles, is pretty nice.

Doesn't normalize enter to BR and I haven't managed to break it. WYSIHTML5 works for normal use cases and produces nice markup but if you mess around with multiple overlapping inline elements or the two lists and indent/dedent enough you'll wind up with very bizarre markup.