This will be a spoiler-free blog, so if you have any spoilers to post, put a warning at the beginning of the comment. (I don't mind spoilers but a lot of people here would)
While I knew the film would revolve around a, for lack of a better term, civil war between the Avengers, I've read a few things that were apparently confirmed in the novelization (and the ones of live action films like Marvel or Pirates of the Caribbean are always heavily abridged and usually useless if you want to find stuff out ahead of time), this film sounds pretty grimdark.
And I haven't confirmed the ending yet, but I've read three conflicting reports. Two of them have to be fake, and one of them is believed to be bad fanfiction, but what they all have in common is that it doesn't end well for the Avengers, who - aside from Black Panther - won't even be appearing in future films (Thor will, but I heard he wasn't in this film). One of them - one of the ones that wasn't denounced as fake but I'm not sure if it's the right one or not - even said an Avenger dies, though as this is spoiler-free I won't say who it is.
Edit: And, from what I read, things go quite horribly for two Avengers
Up until now, Marvel movies, while still PG/13 with language, death, and destruction, have always had some lighthearted elements to it, turned out well in the end, and overall been fun to watch. Even one of the darkest villains, Ronan, appeared in a film that was full of comedy, and they also lightened up the scene where Scott Lang was unable to keep a job. But it sounds like Phase 3 marks the point where it becomes more like the Dark Knight trilogy, which I didn't like because it was too dark and realistic for a superhero movie. I mean, sure, I got into Saw, Freddy, Jason, and other horror movies on my own and loved them, but horror movies are supposed to be dark, they're an entirely different genre.
And people still think these are "kids movies"? This isn't My Little Pony, it isn't Disney movies, it isn't even Star Wars or Lord of the Rings (which were also PG/13). I wouldn't be surprised if the content rating ascended to 14A starting from here, maybe even R. If any one of these endings I read are true, is it that hard to believe that Thanos wins in Infinity War?
People say this is the best Marvel movie, and while I think it doesn't sound particularly appealing to me, I'm in no doubt why - anyone today who isn't in the pony fandom likes their shows to be dark, gloomy, and/or ultraviolent. I don't mind the violence of course but this sounds too dark for a Marvel movie. While others loved this, this could be the part where Marvel loses me, and therefore I don't give a damn about what happens with Thanos anymore, or the other two Infinity Stones, at least The Other died before this point
Edit: OK Why isn't this showing up under "Recent blog posts"?