I wouldn't call psycho a slash and hack. It's more of a psychological thriller.
Hitchcock holds a special flavor and I love it. His movies were a different time and defined what I love about true horror and suspense. Unlike a lot of movies anymore that is just about hack and slash.
quite ironic since his most famous film must have started the hack and slash
On the contrary, he's viewed as the Master of Suspense for a reason. When it comes to the basic terms of movies, they actually do break down quite well. Hitchcock movies build up suspense that leads to a murder or killing scene. When you have movies like Psycho, it's labelled as a Psychological Thriller because it messes with your mind at the same time. The Birds (my personal favorite) is labelled as a Thriller. Most of his fall into the suspense, crime, thriller, or mystery categories. Thus also building a good story with them as well.
Now, a "Hack and Slash" style movie would be like Scream. There isn't no suspense leading up to any killings and there is just blood galore flying everywhere. Other movies like Friday the 13th or Nightmare on Elm Street get broken down into mostly horror with slasher elements. There is no story, per say, with these as the goal of the movies are to scare you and kill as much as possible.
Granted, all the movies can be good in their own light, but it does seem to be more of a trend that the suspense in movies is gone and everyone just resorts to the hack and slash clichae that is now.