I loved this movie as a kid, then I read the book ... which makes watching the movie a difficult experience now. Streiber's novel even draws parallels between the Wolfen and ancient werewolf myths, and their relationship to vampire myths (connecting the book vaguely to The Hunger ... which he later torpedoes when he reveals vampires are actually aliens in The Hunger's sequel.)
Still, Albert Finney and Gregory Hines kick all kinds of ass in this, as does Edward James Olmos.
(Anyone remember Michael Keaton's "Wolfen" spiel from The Dream Team? Easily the best part of that movie.)