If the WotC excerpts are any indication, I'll have both conceptual and mechanical problems with the BoED. Conceptually, it looks like it'll play up the Judeo-Christian ethical and mythological themes already present in D&D, but I'd really like to have seen a more sophisticated treatment of "good." For instance, I'd like to have seen ways for players and DMs to retain the alignment-laden metaphysics that the core rules presume but adapt that metaphysics to other ethical systems with other conceptions of "good". The sanctified spells are especially obnoxious in this regard, and I think it's symptomatic of a real conceptual problem with the cleric: lots of people seem to force good aligned clerics into an almost monotheisitc dedication to "positive energy" and "good" in what are usually manifestly polytheistic worlds. Shouldn't a book designed to fleshing out fantasy conceptions of good-alignment allow good-aligned pagan clerics to be able to be deeply and profoundly good without being righteous in a Christian sense, and to express that good in their spell-casting styles without calling forth hosts of angels or invoking the wrath of the faithful?
Also there seem to be mechanical problems present even in the excerpt, which is never a good sign. The "Lion of Talisid" seems way too good -- pounce at 5th level? And the cleric's ability to spontaneously cast sanctified spells makes an already overpowered class even more powerful by giving it more options.
Of course, there's always the possibility that the finished book will address my worries, but given the quality of recent WotC products, I'm not holding my breath.