Very late to the discussion, as jingle.son and I decided to push watching Part 1 closer to when Part 2 would drop. All done now, and wow... just fantastic.
Now I have all kinds of theories about the nature and existence of the Upside-Down, now that we know why there was a portal there to begin with. Looking forward to finding out. July can't come quick enough.
Mostly just want to point out that somewhere along Part 1, jingle.son predicted that Henry was indeed 001, Vecna, AND little Creel. I'm like "yeah, whatever" 001 - sure, that wasn't too hard to call; Vecna ... maybe; kid-Creel... no way - I didn't think the dates/ages lined up. But alas!
There was a lot that was farfetched, almost too much, but I still enjoyed the fuck out of it. I thought the aging of Mike's actor was the most jarring; Lucas a close 2nd. Really had to park that in the back of my brain, but they both stuck out like a sore thumb.
Also... Eddie will be back. jingle.son has done some digging, and apparently in D&D lore, Vecna has a vampire as his #2 (or ... puppet). Eddie was eaten by bats and his body remained in the Upside Down. Hardcore fans caught puppet and bat tats on him .... it's all connected. MoP as the song wasn't just a random choice.
Perfect cliffhanger .... and yeah, it's gonna be a long wait.