The Radio Times Guide to Science Fiction:

Based on R.Matheson's classic horror novel I Am Legend (as was the weaker The Omega Man in 1971), director Ubaldo Ragona (Italian version) and Sidney Salkow's (US version) atmospheric shocker marks one of the few times in his macabre movie career that Vincent Price was pitted against a traditional "monster" - in this instance people infected with a mysterious plague that has turned them into vampires. Robert Morgan (Price) is appareatly the only living creature immune to the disease, and spends his entire existance rebuffing and killing the undead. But some of the bloodsuckers have found a way of chemically surviving without losing their humanity, and they must erase Morgan, who can't differentiate between the two species. Shot on stark Rome locations (standing in for Los Angeles), Price delivers one of his more restrained performances in this engrossing, superior slice of futuristic horror.