I lucked out yesterday with my pre-order(only person on the pre-order list that managed to get the Dark Edition at Best Buy), but really you aren't missing much.
The box and artbook are the most significant reasons to purchase. The artbook is quite lovely and well produced, and the box is eye-catching with the front window showcasing the framed lion and secret door to access the materials. The included pendant...whatever.
I was more surprised there wasn't much else exclusive to the set though. The game,
making-of DVD, guidebook, map, soundtrack, all seem bundled with the normal edition regardless. Plus, no cover sleeve for the Dark Edition game.
It's not as bad as the Skyrim CE(what was I thinking!), but unless you really need that artbook and huge box to gaze at, the normal edition is mostly the same.