The SFBook Reviews blog has posted a review of The Sixth Discipline. Reviewer Anthony's post reveals the story and characterization didn't resonate that much with him, but it's not a cruel or dismissive review. Even if the book didn't work that well for him overall, he did like the mix of fantasy and technology, and he thought the ending was satisfying.
This is a very well organized review blog, by the way. The books are indexed by author, title, and genre, which is a very nice feature if you like to browse older reviews. There's also a link for free ebooks. Always a good thing!