I'm afraid that on this topic as with many others I have strong opinions. I love a good horror movie which for me means that I hate 98% of horror movies.
The closest thing to a slasher movie that I have ever liked was the original Psycho. Unfortunately most people have had that movie spoiled for them by seeing endless discussions on documentaries that play all of the key scenes over and over. Other than that I like the original Frankenstein, the Bride of Frankenstein and the original Dracula. These have wonderful atmospherics. I like psychological horrors like the original The Haunting, and The Innocents. There is an old Hammer movie called The Abominable Snowman which is a wonderfully eerie suspense piece. The original King Kong is still my favorite especially the island scenes. More modern movies that worked for me include Rosemary's Baby and a comedy called The Fearless Vampire Killers. The Exorcist is a classic but like lots of good horror movies tends to lose its bunch because too many scenes have been replayed over and over on documentaries. There was a modern retelling of Nosferatu the name of which escapes me which was quite entertaining. The Shinning was good when I saw it in the theater but again has been overexposed on TV shows. Most of the slasher movies that make people's top ten lists leave me angry or underwhelmed. They are predictable, employ cheap manipulation and rely too much on blood and guts. The problem with that is that it tends to numb a person so that they require more and more gore "to get off." Movies that make the effort at a psychological twist or in building real suspense get my appreciation much quicker.