3 was kinda in between 1 and 2 for me as well. Much better than 2, still not as good as 1.
I like Hopper more and more, and the grand references to BTTF are amazing for me as a fan (BTTF got me started on Sci-Fi before I became a Trekkie)!
But the big scary multi-legged corpse-sludge monster was too much of a repetition, though it was well made. I liked the concept itself and how it absorbed The Things like a zombie T-1000, but it's like the big bad ships in 3 Trek movies in a row. There was nothing really new about it, so after it had absorbed The Things, it was absolutely boring, and just another monster of the season. I found the suspenseful chase scenes at the fair with Hopper and the T-750 much more compelling. They should actually cast that guy in a future Terminator, he did a great job!
I was a bit unclear on if those people taken over, or duplicates of people who were then kept in storage by the midflayer. Duplicates made from its own body that it had constructed out of rats.