This suffers from the same problem as a lot of Stephen King adaptations, in that it's very low budget. It's an expected result of his novels being available for use in movies and television series basically for free, since the same people who can't afford special effects or a good filming crew are also going to be attracted to the low cost of basing their work on his novels.
So yes, the effects, shooting, and editing are generally of poor quality. If you go into it expecting it to look like something that enthusiastic drama club kids from high school would put together, you won't be disappointed. The casting and acting is surprisingly good. The dialogue isn't bad.
The script deviates a lot from the book. In some ways that's a good thing, because the book was written 37 years ago, and elements from it would not have made sense in a modern series. It's also an improvement that there's more than one band of survivors in a single location. Changing the lead character's young son into a teenage daughter is also an improvement - while having the little kid to protect gives the protagonist an automatic moral high ground, he would have been annoying in a movie.
Some are criticizing the social themes, but those themes are very much in keeping with Stephen King's general work. He is all about small town dysfunction, hypocrisy, and even insanity. So I don't think the various issues regarding sexuality and bullying are even slightly out of place, even if they obviously weren't a focus of the novel.
But there are a few changes that don't work as well. Why does this small town have a huge indoor mall? How can the mist both be mysteriously related to a nearby army base, but also have happened 150 years ago? And they may have made a mistake in transforming the mist from a straight-forward mist with lots of monsters, into something that has a bit of a life of its own and seems to hold personal delusions which other people can see and hear. The Arrowhead guys are also completely lacking any subtlety, and appear to be extremely stupid. Some of their actions are undoubtedly intended to make the situation seem more serious, but since their characters have no substance, they come of as daft and impulsive instead.
But ultimately I'm going to keep watching it, and I hope there's a second season. It would be interesting to see where or when (or if) the mist ends, what's up at Arrowhead, who the amnesiac really is, and if everyone gets what they deserve.
