Well, I've got the DVD and I've watched Volume 4 as a 'movie' a couple of times now.
My reaction is that Volume 4 is actually a lot better than it felt watching the episodes individually via the web. Watching each episode individually, particularly with the gaps between the release of each episode, made the volume feel awkward and slow. And I didn't like the separation of the characters.
Watching the entire volume in one sitting, as a 'movie' rather than episodically, made the volume feel a lot faster and more coherent. Although there's still a sense of the volume as filler or prelude, I am now very much looking forward to Volume 5.