I saw INSDIDIOUS: CHAPTER 3 (2015) the other day, I put off watching it as the second one wasn't as good as the first. This thing is a prequel that takes place before with an origin for the ghost detective people. It actually was a "jump scare" type movie that was pretty much in the same style, it got me a at least 3 times, so if thats you're bag then I'd recommend it. Otherwise, it gives an okay cast with more of the slick ghost world "The Further", darkness with random ghosts stuck in parallel real world pockets, and a few doses of teenaged girl blather.
Its got the principle of ghosts that had a messed up existence are now demons thing going like the others but this time their classifying this as a different case than a possessing (magic jar) demon like in the other two films.
I finally watched the first INSIDIOUS (2010) movie. I kept feeling like I'd seen it before, and then I remembered POLTERGEIST (1982). It was well done, but felt like a remake and a bit paint by numbers with the baby monitor, sounds in the attic, and figures glimpsed in the background. The 'gas mask' that the demonologist wears is very reminiscent of what Dream wears in Neil Gaiman's THE SANDMAN. There sure were a lot of violin strings, so much so that it seemed heavy handed and distracting -- I get it, I'm supposed to be scared here, you can ease up on the violin! My favorite parts were the way the ghosts were portrayed with an almost stop-motion fashion in "the Further." The best scare to me was when the alarm went off and he walks down the stairs to see the front door wide open... If you weren't yet convinced it was supernatural, you would be sure an intruder was in your house at that point! That would be scary.