I wasn't terribly enthused by the first episode... two guys with no introduction both getting medical treatment from indians in very dark scenes = confusion. Plus, the early episodes have a lot of exposition, then the more impressive actions scenes start showing up in later eps - not an ideal way to hook the viewer. But once the characters start getting fleshed out, it becomes a very well-made, interesting western.
It's not terribly original, but it being a limited series rather than a multi-season one means that the stakes are raised, as characters may or may not survive. This led to some surprises in both who lived and who died, which helped keep my interest high.
Basically, if you like westerns, you're going to like it. And if you think it's visually strong early on, wait until the finale. It features some of the most beautiful scenes I've seen in a long time.