I enjoyed CoG, and I agree: it does have the narrative density of a novel. It had some genuinely intriguing plot points that have very promising trajectories, but as a Harry Potter film, I find it rather problematic.

Conceptually, it's being pitched as an extension of the Potterverse, and naturally perceptions and impressions of it will leverage and build on what audiences are familiar with and thus to some ostensible degree, their expectations. When something is marketed as a HP film, there are expectations and many (I'm making an assumption for the average viewer/fan) anticipate hallmarks/markers of a Potter film that builds on what they are already familiar with. As many have mentioned, it's problematic that it's pitched as a Potter film and yet its narrative line runs quite independantly from the original films.

It's precisely because some audiences expect a lot of Rowling as a story teller that the inconsistencies and departures from canon become all the more stark and troublesome because it's not what they have anticipated or are familiar.

Don't get me wrong, I like the film, the film had some incredibly riveting action scenes and fun character arcs, but I can definitely see why people are upset with it. It's dismissive and disappointing to see people flame it mindlessly and to completely disregard it, but I could definitely see why they're upset.