I always used to find most Westerns dull (sorry Dad!). This one certainly isn't, even though there are long stretches with nothing happening.
The basic plotline is that rancher Christian Bale has to get the evil Russell Crowe onto a prison train. There's a lot of well done action - the body count by the end is huge, but at it's mostly an exploration of the psychology of the two men.
Bale is playing a man who is desperately trying to look after his family, but more than that, he seems to be trying to search for meaning in life. Crowe is playing a completely lawless villain, who has no qualms about killing anyone but spares some. At the same time, he is an artist who has an incredibly charismatic personality and an interestingly ambiguous relationship with God. He recognises that he is completely evil and only ever acts in his own interests. He loves quoting Scripture, but expects to escape God's judgement. But is he wholly demonic?
Anyway, I enjoyed the film. It's really well made and well acted, and everything makes sense in the end.