I watched 'Hostiles' soon after 'Woman Walks Ahead' (http://trakt.tv/movies/woman-walks-ahead-2018), because, chronologically, it picks up immediately after the events depicted in that film. The two films are very different, but they'd probably make a decent 'Twilight of the Frontier' Double Feature, so you might want to consider pairing them up.
Make no mistake, though, this is a frequently brutal film. When two children and an infant get murdered within the first four minutes, you know you're in for a hard ride. But I would still encourage you to take that ride.
A few reviewers I've read have called this film 'clinically depressed', or 'unnecessarily grim', but I never found it anything less than realistic in depicting both PTSD and the phenomenon that modern psychiatrists refer to as 'moral injury'. This film is ruthless in its depiction of what unceasing senseless brutality does to both the psyche and the spirit. We witness soldiers compartmentalizing and rationalizing their actions, or struggling with the cognitive dissonance of a fractured soul and a shattered moral compass. Perpetrating or bearing witness to acts that ultimately transgress one’s deeply held moral beliefs is a very real and crippling reality, and this film effectively depicts that, in a era long prior to any social awareness of it.
Both Christian Bale and Rosamund Pike have perfected their thousand-yard stares, although each of their characters have earned them through very different means. It may be easier to be sympathetic to Pike's character — who has suffered so much — than it is to be sympathetic to Bale's — who has himself caused so much suffering — but the film asks us to feel for them both, and I think it succeeds.
The only place where I feel 'Hostiles' goes a little wrong is when it tries to take what should remain subtext, and forcibly makes it text. For example, when a regretful cavalry soldier approaches Chief Yellow Hawk and says, "Our treatment of the natives cannot be forgiven. Have mercy on us," it comes across as something that the audience shouldn't need. We know the character; we know he feels that way, even if he never expresses it. A sentiment like that, however true, should remain subtext. Maybe the filmmakers had doubts whether the audience could receive it as subtext, but the result is a little patronizing. It's similarly over-done when we find ourselves sitting through scenes where characters monologue at length about racism, vengeance and soul-destroying regret. We get it. You don't need to be quite so ominous about it. Maybe trust the audience to appreciate what kind of existential journey you're inviting them on.
Despite those mis-steps, I was deeply moved by 'Hostiles'. It could be one of Bale's best performances yet, and it definitely ranks as Pike's best work so far.