Finally, a response from one of my readers!
I don't have all of his comments back in the mail yet, but (via email) he felt as though the characters were real people, and he wanted to read more about them at the end of the book. I'm so thrilled, b/c (as a reader & writer) character is the most important element of fiction to me!
He also had several solid suggestions for improvement (regarding certain scenes being over or underdone, not enough plot hints given, and areas he would have liked to have read more about).
One critiquer down, five to go...