This series is part of my reading challenge for later this year . The first few books (maybe 5 or 6) will be rereads, and I just pre-ordered the paperback edition of
A Perfect Blood (The Hollows #10), which is supposed to come out on September 25th.
To answer your question, I do remember their getting better, darker and more intense with each book. You feel (for better or worse) for all of the characters, and some who seem minor at first grow to have major impact later on.