John Carpenter's Halloween is often credited as the film that created the slasher genre when what it actually did was made it popular. Sometimes Alfred Hitchcock's Psycho is credited for inventing the slasher genre but that's a thriller film that just happened to have a knife as a murder weapon (an often used weapon in slasher films). The blue print for all slasher films to follow was created by Mario Bava in The Bay of Blood, if it did not invent the genre, it's certainly an important film that clearly influenced the slasher genre for many years to come.
Mario Bava is one of the three famous Italian directors who excelled greatly in creating Giallo horror films and A Bay of Blood is regarded as Bava's most famous work and certainly his most violent. With 13 grisly murders involving knives and machetes the film met the wrath of the British censors who quickly banned the film (along with many others) as they objected to its most violent sequences.
Anyone who knows what to expect from a Giallo horror film is very much ready for one of Bava's finest films. Giallos are famous for their gratuitous and unnecessary nudity, extravagant death sequences, bad dubbing and horrendous acting all of which is found in A Bay of Blood. For this reason Italian horror films from this era a very much an acquired taste, those who aren't fond of the genre (either horror or Giallo) will find very little to stir their interest, however those who lap this stuff up like a thirsty dog will find Bava's A Bay of Blood to one of the finest works of the genre.