I think the episode, except for one dubious choice at the end worked really well for me. From a dramatic standpoint, Eleven/Jane hiding out in the cabin until she could be drawn back into the main storyline is not interesting. I wanted to see what would happen when she encountered her mother and was able to understand what Hopper meant when he told her she wasn't around anymore. I largely enjoyed the way it introduced Kali, though I'd be happy if the other characters in her storyline would disappear. I liked the fact that she had two very different opportunities to find a family and had the awareness to see why neither would really work out for her. As well-meaning as her Aunt is, it's not really in her wheelhouse to be capable of protecting Jane, she couldn't even manage to be appropriately discreet when she left a message for Hopper. Kali and co. are just big trouble.
Kali is quite destructive (the name choice seems very deliberate) and is on a path that will probably lead her and those with her to death or, possibly worse, capture. I can't say I greatly disapprove of her mission to rid the world of some genuinely evil people, but, as Jane grasped fairly quickly, life is too complicated for something as simple as revenge to set things right. She's not a good person for Jane to be around right now, although I think Kali genuinely cares about her, she's too manipulative and angry to do anything other than put Jane in danger, both actual and moral. I think they are underlining fairly heavily that the older girl will have a continued presence on the show by emphasizing that they are sisters, especially with Jane's mother supporting the idea. No matter what Kali tried to claim, I don't think Jane's mother wanted to her to find her sister because she wants revenge. I kind of doubt she knows what the girl is up to, I do think she wanted for her to be alright and for Jane to find her because hopefully together, they could keep each other safe. I didn't see anything about Kali that suggested spin-off, her mission is not that interesting a premise and the characters she was with are dull and disposable. I could only remember the name of one and that's only because I heard it so many times with in the episode. Axel, AKA Mohawked asshole who seemed to have accidentally wound up in the wrong warehouse on his way to join Clarence Boddicker's gang. I was expecting and frankly hoping he'd die in a hail of bullets while screeching "Eat hot lead! Copper!!!" well before the end. He very nearly didn't disappoint. Almost as obnoxious was the ratted-hair loudmouth girl, and of the two remaining, large folded-arm guy, barely registered as a presence at all and only getaway driver chick seemed like someone capable of doing a passable impersonation of a decent human being with dimension beyond "lets wreck stuff, and take down the man, ma-aaan.". Kali's merry gang of miscreants can go away , never to be seen again, and I hope they do. Quite possibly that was exactly how I was supposed to react to them.
I was intrigued by what Pruitt Taylor Vince's character said about Brenner. I think his death was fairly unambiguous, I really don't expect him to pop up as anything more than a figment of Kali's powers so I think the claim he's alive was likely nothing more than a desperate man trying to stay alive. However, if the upside down is a parallel dimension that is crossing over, could that meant that in a way the head Demi-gorgon is related to the evil Brenner put out in our world, that in a sense an aspect of him still exists? Even without that possibility, I thought it was interesting that Will referred to the main presence of the hive-mind as "he" as opposed to an it or even a she, as the head of a hive is usually female.
My biggest problem with the episode is the point in the timeline that Jane realizes Mike and Hopper are in danger. At that point they are literally minutes away from a swarm of demo-gorgons launching an assault from within on the facility. She has to get to an intra-city bus, take the bus, make her way through town to the facility before she can even hope to help them. That seems like it could take a few hours. Even if she'd instead persuaded Kali's bunch to drive her with the pedal to the metal, it seems like an awfully long time would pass. It would have worked better for me if she'd realized the potential danger when it was a little less imminent at an earlier point in their timeline before it was obvious to them. I'm hoping the attack has a fairly long timeline so we aren't taken out of things by her arriving in the nick of time mere minutes after things go horribly wrong at the lab. This show is quite good about avoiding those sorts of sloppy writing mistakes, so it would be quite a shock if they drop the ball like that.