Barlow's basically Dracula. You sort of wonder why King didn't just name him "Dracula" and get it over with. Maybe he felt that'd be silly. Or maybe the townsfolk would have been put off.
Anyway, Barlow's pretty nifty, as far as supervillains go. He's got some good rants, like when he tells Corey Bryant that Americans, and especially small-town Americans, "spill each other's blood with great vigor" (10.324). He's got some good boasting threats, too—especially in his letter to the vampire hunters, where he promises to castrate Mark and declares, "I am not a serpent but the father of serpents" (14.277). It's not quite "Children of the night; what music they make"—but it'll do.