Corny
This really doesn't hold up well. The scene where Pennywise grabs Georgie's arm and it zooms in on his face as his teeth change just looks laughably silly. I also think that they showed far too much of the clown. He doesn't appear nearly as much in the book, which makes him much scarier.
While I did think Tim Curry did a nice job playing Pennywise, I felt that he was just too goofy to be scary, especially during that library scene in the second half. There is a similar scene in the book but it's much darker and more sinister.
Now say what you want about me, but from what I've seen of Bill Skarsgård's performance, he makes a much better Pennywise.