Pennywise wasn't revealed to be a spider-thing is this movie. That said, one of the points of this movie is that the Losers never killed IT, just drove IT away into hiding for a time, even though they hoped IT was actually dead. Probably one key to killing IT will be breaking through to IT's true physical form, which is perhaps that of a spider-demon and perhaps something else. For my part I liked the movie even with the stuff that was left out (and quite a bit of stuff was left out, including, thank God, the weird child-orgy scene from the book). I will say that the movie kind of over-simplified things with the kids dealing with IT. In the book the kids developed a bit of understanding of IT's nature to the point that they were able to "weaponize" their beliefs to use against IT. The movie falls back on the "don't be afraid/friendship is magic" kind of thing which makes the kids' triumph here seem a little less earned. Still, overall I liked the movie, liked the young actors in the movie, think the best thing for the kids would be to move out of town and sterilize the place with a nuke and am looking forward to seeing the next installment of the movie once it's made in a couple-three years.