I don't even know what the disagreement between a teaser and a trailer is anymore,because this is the first official trailer for It, but it's also shorter than some of the teasers. Let's just assume the Hollywood marketing department has no conception what they're doing at this point. Anyways, and they seem to be leaning a little heavy on the jump scares,but it does recognize like some effort was put into actually generating an atmosphere of dread. It actually feels like a proper horror movie up until the last fifteen seconds when the trailer-making-people decided to just turn it into another cookie-cutter horror trailer. Gotta acquire loud noises and a scary looking thing running towards the camera! That's what audiences appreciate!
Source: iwatchstuff.com