I grew up watching these in the late '60s and '70s, and got to see a lot of them in theaters. There is a progression which you can experience, watching the films in chronological order, and even though the overall quality of the films drops in the '70s, there are still some gems (like TWINS OF EVIL, CAPTAIN KRONOS: VAMPIRE HUNTER and FRANKENSTEIN AND THE MONSTER FROM HELL).
Besides some of the wonderful books on Hammer Horrors currently on the market, there's the exhaustive and exacting, but never boring, <i>Little Shoppe of Horrors</i> magazine, which has been in publication for over two decades: http://www.littleshoppeofhorrors.com/