I read the book a few months ago, and I have to say I like the original miniseries better as an adaptation. I think the 50s and 80s settings are important, and modernizing the story takes something away from it. Also the way the original miniseries framed the story similarly with flashbacks instead of linearly feels more in line with the book. Overall, both adaptations made deviations, but the deviations in the original are more forgivable IMO. Tim Curry's performance is far superior, and is one of the great horror performances of all time. The acting from the kids in the remake is better, but they feel like more distinct characters in the original. Richie, Stan, Eddie, and Bill all sort of blend together in the remake, their personalities don't feel distinct enough.
I'm very excited for the second part though. I hope that eventually we will get the perfect adaptation of this story. I think the correct way to adapt this is a big budget miniseries.