Yes, horror movie posters can be works of art. One can imagine this was the scene for those soldiers left behind after the first disastrous encounter with the Xenomorphs in Aliens. Disturbing and beautiful.
It would've been so easy to promote this film with the scary image of Pennywise taking up the entire poster. But subtlety is often much better. In this case they take elements from one of the story's memorable early moments and give us a very disturbing design. Half hiding the clown's creepy face within the balloon is definitely a case where less is more.
Even without the open heart surgery there is something eerie about this artwork. The porcelain-like Jennifer Lawrence just seems a little too perfect to be real, crossing into the uncanny valley. Then add in the element of a mother literally offering her heart to someone and you've got one memorably disturbing design - even if it would likely never find itself on the walls of a multiplex.