The Good: From the beginning of this episode, what worried me was that Will was going to come back from his (well-meant but) ill-advised attempt to confront the Thing In The Upside Down as completely possessed. The fact that he did not was a great relief. Such a thing, making Will a possessed victim, would have been a bad choice for two reasons: firstly, it would have been far too easy. The possessed child trope has been overdone in horror because it’s a gut-wrenching paradox: the evil that is at the same time innocent. It’s sort of the opposite of the zombie trope: rather than the enemy you get to kill with no moral qualms, it’s an enemy you have to kill despite the moral horror of it. It’s a spiritual hostage crisis.
Secondly, Will’s role in the series up until now has been almost exclusively that of the victim, despite his attempts to survive. Giving “Will the Wise” the agency of spying on this “thing” is a way to make him truly a member of the party rather than its quest, and makes him a better character.
I’m also amazed at the way they handled Nancy and Jonathan’s plan to reveal the truth behind Hawkins Lab’s cover-up of Barb’s death. It’s becoming plainer that Paul Reiser’s character is not a reprise of Burke from Aliens, but rather a sensible man who is being as honest and kind as he can while at the same time being as deceptive and hard-nosed as he needs to be. Most series would portray anyone in government service as being evil by default, but once again, the writers refuse to take the easy way out. I love it.

The Bad: I have to admit that I found it really weird that, given the way Will is talking, his friends and family did not come to the conclusion that heating Will up, with or without his cooperation, would have been a good idea.
Also, Hopper not telling El the whole story about her Mother seemed to me rather gratuitously clueless.
But the worst part of the series is also showing up here because I find Dustin to be uncharacteristically dishonest and clueless about Dart for no real reason other than to build up tension. It’s the sort of cliché the series has done well to avoid: The Protagonist Keeps A Secret He Shouldn’t.

Further Questions: What will El find when she goes to see her mother? What will Nancy and Jonathan do with their knowledge. And most importantly, what is up with Max and her weird brother and why does he think it’s her fault that they are stuck here rather than in CA?