Great for preschoolers if you can fast forward or mute . . .
Our daughter, who is almost 4 watches very few children's shows, none of them violent. We've watched the entire Planet Earth series with her and she loves it (and so do we). When we see what appears to be an intense predator/prey scene with her, we mute or fast forward. She lets us know what she's comfortable watching, or not.
I think it's good to inform children early about the circle of life, as well as the fact that when we human beings eat meat, animals are killed. This show provides a forum for doing that, among other things.