I think you have to taken into account that this art is meant to be "generic" D&D. Without a setting attached to it, they have gone out of their way to emphasize the new high fantasy look of out-of-the-box D&D. Nobody is saying that your campaign has to look like a laser-light show.
Although, truth be told, with all the spell effects and magic weapons, this probably IS what a typical mid-level party looks like.
I love the white space. Yes, they are not filling every page to the brim, but they don't really need to. Design-wise this is much easier on the eyes and the brain. Plus it is an acknowledgment that the PHB is not the last word on these classes, races, etc. You know they are making more books with more options for these and other classes so why crush too much information into the first book? The 3.5 PHB is a very efficient tome. I don't think there is a single blank spot in the entire book. And reading it hurts. Do you realize that at one point in the book you can go more than 25 pages without a single illustration? There are maybe 6 bad pieces of art in the entire section of this book on spells in over 100 pages. That is crazy. Yes, they have given me the text, but they have given me NOTHING else.
Honestly until flipping through the entire 3.5 PHB right now, I had no clue just how ugly and utilitarian it is. Why would ANYBODY who wasn't already a player who flipped through this thing at a store take it home with them? This is a 316 page book completely lacking in AWESOME. I always liked the hand-made covers, but that is where the creativity started and stopped.
Design matters. Not as much as whether or not the rules are good, but an ugly book does not inspire me to play it no matter how good the system might be. These shots from the new book make me want to stop what I am doing and play D&D.
Jaime