I just saw it today, and I kind of agree with everyone else's posts. Random thoughts:
I felt similarly after watching Hereditary, in that most of the film felt genuinely tense and foreboding, but it didn't quite stick the ending - it sort of tilted over from frightening and disturbing into the ridiculous at the conclusion. Although I enjoy a slow-burn, it was a bit overlong and needed trimming.
I didn't know exactly what would go down (I assumed ritual sacrifice of some sort going in) but I immediately knew the poor British couple were effectively the movie's "red-shirts", along with the rude transgressors. I think the tension for me was whether the main couple was going to try and make a break for it or not. (Did anyone else think the actor playing the non-committal boyfriend looked EXACTLY like a thinner fitter Seth Rogen? Was it just me?)
I agree with everyone else about the winking flowers - it added to the trippy hallucinogenic quality of the film. I wonder if the timing being all over the place was also meant to sort of scramble the audience's brains? It was supposed to be a Midsummer festival which one would think would be Summer Solstice which is late June. Yet they're crowning a May Queen. And a bunch of trees had pink blossoms on them, which even in Northern Sweden seems too late in the season. I dunno.
I felt saddest for the poor bear in the end.
One thing that has bothered me about both Hereditary and Midsommar is Ari Aster's seeming fixation on people with physical deformities. I thought Millie Shapiro (the little girl in Hereditary) was just unusual looking, but apparently she has an inherited condition that affects the cranium, and again in this movie, someone with a visible deformity was used mainly for horror purposes. That doesn't sit well with me.
I will say kudos to the production designers and costumers - they did a fantastic job of world-building with the folk-art paintings, runic symbols, embroidery and flowers. For such a freaky film, it was visually beautiful.
Can't say that I loved this film, but Aster is very good at using horror to explore grief - however I thought The Babadook dealt with that theme more effectively. This one was like an updated less goofy Nordic version of The Wicker Man.