It seems to me that most of the five star reviews for this movie are based on a nostalgic connection to it, which is completely understandable, but as someone watching it for the first time in my 20s, I don't feel I got as much out of it as those who might have grown up with it.
I think the main negative that people point out is the lack of real plot; stuff happens, sure, but nothing that interesting or that moves the plot forward all that much. The bullies aren't unlikeable in a fun, villainous way, they're just plain unlikeable and I was glad whenever they were off my screen. The chemistry between the kids, however, who I will say are all written amusingly realistically for boys their age, is definitely the highlight, especially the bond between Gordie and Chris, and I was genuinely moved by the scenes where they opened up to each other, but beyond this, there's really not that much going on. If you're a big fan of character over plot, though, I do think you might really enjoy this movie.
The main issue I have is with the ending, which just didn't make sense to me. Of course, you could argue that there is a sense of realism to it, but without spoiling anything major, I felt personally that Chris' ending in particular just felt unnecessary and negated any character growth or progression we saw for him. I felt a little deflated when the credits rolled, and I think a much more poignant, lasting message could have been created had the ending been a little different. Instead, I was left feeling that what I had just watched had not been unenjoyable by any means, but ultimately just a little bit pointless.
TLDR: A well cast, mostly enjoyable film, though much more character driven than plot driven. Realistic writing, though the ending was a little disappointing.