I heard a lot of good things about Demons, but I thought the movie was only decent. It's a lot more original than the majority of brainless Italian horror, with the evil movie theater and the events in the film becoming reality. Yeah, there's a few gore scenes but nothing jaw dropping.
I far prefer Fulci's zombie flicks or Cannibal Ferox/Holocaust to Argento's style. Demons is missable, if you are a die hard Italian splatter fan then rent it.
It's easy to see why American horror flicks from the 80s are more popular than the cheap Italian knock offs.