Insidious is the cinematic definition of ‘a game of two halves’. An extremely tense first half gives way to a nearly laughable second.
The best analogy I can think of is that when you saw Alien for the first time. The Xenomorph was a terrifying, deadly, and mysterious presence. But by the time we got to Resurrection, and saw them in all their glory. they have become characters themselves. Once you see the strings being pulled it stops being scary.
Frustratingly the characters are well written, but it’s never good when you’re laughing at the antagonist.
Sometimes insidious, sometimes insipid.