I'm a big Kevin Costner fan and respect the fact that he put his money where his mouth is and financed his dream project himself, but Horizon: Chapter 1 was one of the worst theater-going experiences I've had in awhile. Overly-long doesn't adequately describe how tedious this bloated prologue of a film is. There are at least 5 distinct plot threads the film covers but none of them are ever given even a modicum of development. There are also some troubling stereotypes and tropes at play that make Yellowstone look progressive. The production values are incredible, on par with any big budget Western ever made, but this is the kind of drawn out nonsense that plagues prestige TV lately, and it's inexcusable on the big screen. I wanted to support a filmmaker putting everything on the line for a theatrical experience, but unless the reviews are better for Chapter 2 I won't be seeing it in theaters.
Also, another nitpick I had that has nothing to do with the film itself, but the theater I saw it in projected the image very dimly; the bulb must be on its last legs. Obviously not Costner's fault, but it did make the nighttime scenes even harder to see.