As a broad rule of thumb, horror is like making a roux. you add the unheimlich to the heimlich steadily & make sure it is mixed in, otherwise you get lumps

So for example Alien establishes a nice little core of the heimlich (our very human crew) and adds alien threat to the mix a bit at a time: signal, derelict, space jockey (alien but not threatening), facehugger (threatening but circuitously), chestburster, xenomorph

We are shocked and horrified but we are always shocked in ways we can assimilate into our growing understanding of what is going on. Our roux thickens without becoming lumpy.

Every event ups the ante in one way or another: we LEARN things while we are being horrified, so however viscerally shocking a given event may be, it contributes to the deepening dread of the overall situation.

So the simple horror of being unable to get the facehugger off is compounded by learning about the acid blood; the horror of the 'cattle prods' proving useless is compounded by realising the alien has grown staggeringly fast

What you do NOT do when making a roux (or custard, or plaster for that matter) is eagerly dump tons of powder in and stir like mad in the belief this will give a super result super fast

It will not, and you end up with unassimilated lumps of arbitrary weird in your mix

Hellraiser is a counter-example (I consider it carnal fantasy rather than horror per se) but in that situation the protagonist is the flour being added to the molten butter of Clive Barker's imagination

But anyway. For me the difference between Hereditary and Midsommar is that the latter succeeds in adding its flour steadily over time while the former does great until halfway through & then starts frantically tipping more and more flour in until what's left is a lumpen mess

Part of the reason the shocking mid point of Hereditary works so well is that it shows the effect upon the family entirely plausibly. It stirs the flour in with an expert hand. Can't fault it.

But by the time you get to people bursting into flames and levitating, it's all lumps and no sauce.

UNLESS you are one of those fortunate viewers whose molten butter is copious enough to absorb all the flour

So I think this is the crux of why some people are convinced Hereditary was brilliant and others are equally convinced it was a bag of arse

It's all down to how much molten butter you bring to the pan

this has been the roux theory of horror film dynamics, please add grated cheese to taste!