Hawksmoor - Peter Ackroyd
Quite excellent. The evocation of atmosphere is fine, the ideas are subtly presented, and the author does a remarkably fine job of creating 17th-century language. This story walks a razor's edge between "subtle" and "obscure", but stays on the right side; I didn't fully appreciate it until a second reading, but the first reading was gripping nonetheless. Admittedly, Ackroyd's misanthropy can be unpleasant (as I've found from his other books), but it's part of the power of Hawksmoor.