When I read/hear what people thought of the mini-series in 1990, usually those who were kids at the time liked it, while King fans who were already adults back then thought it was quite lame.
Anyway, there's room for both adaptations to be bad. Both omit the back and forth structure of the book and opt to divide it into part 1: the kids and part 2: the adults. But the book's interwoven structure is what makes it's themes work and justifies why we can experience both confrontations without it (and the rest of the adult parts) feeling repetitive. This needs to be a 10-16 episode event series to adapt it properly. I like chapter 1, but it feels so rushed. It doesn't have time to let the character development and creepiness breathe, and doesn't feel like the story takes place over an entire summer.