I really enjoyed Cowl. I'll admit that it took a while to get into, but once it "clicked" with me I loved the hell out of it.
(And without spoiling the ending, it does rather seem to set up nicely for a sequel Neal. Hint hint hint...)
I keep meaning to write a review for the reviews forum, but one of the most interesting aspects of the book was its take on the mechanics of time travel and the nitty gritty of how you go about altering the past without ripping a gaping orafice in causality.
I've tried to write time travel fiction myself and know how easy it is to tie yourself up in knots with that stuff, but Cowl manages it quite elegently, IMHO.