The blurb is just dishonest:
_To put their demons to rest once and for all, Josh Lambert and a college-aged Dalton Lambert must go deeper into The Further than ever before, facing their family's dark past and a host of new and more horrifying terrors that lurk behind the red door._

In order of the claims:
They don't go deeper into The Further than ever before--they literally go to the same places they've already been, and not as deep as they have been in previous movies.
They faced more of the family's "dark past" in the second installment. In this one, they only revealed one thing that's barely a spoiler: [spoiler]Josh's dad could also astral project into the further and was really upset about it. But not enough to actually matter to the plot.[/spoiler]
There wasn't a "host" of new and more horrifying terrors. First of all, there were only two "new" terrors, who turned out to [spoiler] not really be terrors at all. Just a puking ghost who was upset about the door being open for no explained reason and Josh's dad.[/spoiler] and the red-faced demon again. The main antagonist was literally just the same antagonist again.

The movie merely rehashed the same villains, discoveries, and threats faced in the earlier entries because of the incredibly useful trope of "forgetting" that the previous movies happened. It had a promising start which is the only reason I've generously given it a 4, but it very much did not deliver.

A cheap ending to a franchise I love.

Terrible story, they erase the character's memories in the very first scene and then we spend most of the movie trying to get those memories back. It's frustrating, annoying and the characters are made dumb because of it. Basically, it took way too long to get back to where we were at the start. Eliminate that unnecessary plot and you don't have much left. Which is why it feels like nothing happened. It takes so long to get started too, a solid 40 minutes with no scares. On top of that they didn't even bother giving the entity a backstory. Every *Insidious* movie gives a story to their villain, however small it may be. Absolutely nothing here. Elise's story looked promising at the end of *Chapter 2*, well it's as if they said "never mind that" because she only gets two scenes and they're completely unrelated to how things end for her in *Chapter 2*.

What worked well is Dalton (Ty Simpkins) he shows that he's capable of carrying the movie on his own and I like what personnality they gave him. Some of the father son dynamics were fairly interesting but that aside, Josh (Patrick Wilson)'s story felt pushed and what's with his father scaring the shit out of him by running through a window only to later appear as an angel. What happened between those two scenes to get to that? Chris (Sinclair Daniel) was by far my favorite, her comedic relief was welcome. I believe she takes on the role of Specs and Tucker here. The one scene they had was awesome, I hope they get a spin-off.

The paintings: those were fabulous, creepy and I only wanted more of them and that weird teacher which the movie completely forgets in the second half. I won't complain about the jumpscares sinse they've been part of this franchise for a while but some of them were incredibly cheap and predictable. Every scene with Darth Maul was genuinely scary though and i'm not sure if him being scary is just PTSD from watching the first. Too bad he was barely in the movie. The possession scenes are the most memorable and I like how they beat the entity. It just feels like it happened too fast and I couldn't believe the movie ended when it ended. It's all due to the first 40 minutes being scare free and long to get started.

"Dalton" (a competent effort from Ty Simpkins) and his dad "Josh" (Patrick Wilson) have a strained relationship as they come to terms with recent family upheaval and that pressure is beginning to unravel the hypnotism that is protecting them from even more ghastly memories from nine years ago. At college, he quickly befriends the quirky and outgoing girl "Chris" (an overpowering Sinclair Daniel), who is wrongly assigned to be his room-mate. Before long the pair are mired in a series of mysteries that seem to emanate from his imagination - a comatose state sets in and another dimension - and it's perils - arrives to terrorise the family via an ominous looking painting that he has instinctively created and hung on the wall. Can they unite, put their differences behind them and rally to defeat their nemesis and close the portal for ever? Well, sadly I didn't really care. This is really just a revamp of the first "Insidious" (2010) film with some added teenage angst, familial discord and little enough by way of contributions from the other siblings to give any depth to this routine father and son drama that save for the slightly livelier denouement was really rather predictable and dull. There are a few jump moments mid-way through the drama, but for the rest of it it seems that Wilson was perhaps too preoccupied with both of his roles here to focus properly on either, and that leaves us with a rather unremarkable muddle of a film that I'm afraid is just instantly forgettable.