Justin Turner’s review published on Letterboxd:
If you're a fan of its two predecessors, chances are you will find enjoyment in Fear Street Part Three: 1666, but for me, it's more of the same, a bunch of mediocrity.
As the title suggests, around a little over half the runtime is spent in the year 1666, and to put it bluntly, it was rather dull. But to be fair, it's very challenging to make period horrors engaging.
I get it's a vision, of sorts, but it was an odd choice to have characters from the first part reappear in this film as different people with period costumes and bad accents.
Regardless, it does tie into the first film, and the reveal about the origins of the evil made my eyes roll. Both contrived and predictable. Not even the mythology makes a whole lot of sense, but it's whatever.
The third act provides some campy slasher elements and light humor. The main takeaway you will get in the film is that the modern sequences triumph all.
One major nitpick of mine, and it happens in a lot of slashers, is that when the antagonist has the chance to kill the protagonist, but of course, this person has to give a speech, which gives the other person enough time to either escape or kill the antagonist.
And it happens here. Again, some may call it a nitpick, but it bothered me.
Anyway, as a trilogy, I will forget this in about a week. It didn't take as many creative risks as I wanted; the character and narrative structure are very bare-bones and formulaic—lots of subpar performances. The R-rating did provide some value in terms of the violence, but not enough to save it overall.