I've seen Vampiros Lesbos (1971), which i didn't like, and three fairly decent ones: Miss Muerte (The Diabolical Dr. Z / 1966 - script by Jean-Claude Carriere), Les cauchemars naissent la nuit (Nightmares Come at Night / 1970), and Faceless (1988) . After seeing these three films, I must say I'm somewhat fond of Franco and plan to see more. 

I especially loved the play of shadow and light in Miss Muerte and its Vertigo-like touches, as well as the fairytale atmosphere and the beautiful photography in "Nightmares Come at Night".