Honestly, to me that was what made at least the costume for Pennywise better in the original mini-series. It was subtle. If you didn't know the movie and just glanced at a picture of that Pennywise, you'd think he was just a clown. To me, that was what made it so much more sinister. The fact that he just looked like a clown... but was pure evil and was doing all these really horrible things. Of course, the more monstrous face (when he gets the red eyes and sharp teeth) is cool too, but to me the creepiness of the old design was just so much more subtle.
From the first moment I saw it (way before the movie was even out yet) I thought the new design for Pennywise just looked too obvious. It just screamed "I'M SCARY" It lacked the subtlety that I think actually makes the creepiness/scariness so much more effective. I mean, at least given that sort of monster. It isn't like I'm saying all monsters should be like that. Wolfman shouldn't look like an adorable cuddly puppy until he bites your face off. LOL! But for an evil clown... it's a little MORE creepy/scary when he otherwise looks like just a normal clown.... until he bites your face off.