This is a very good introduction to Sioux history, from Prehistory to today. It's not often that you find a history of the Sioux Nation spanning from so far to so close. It follows all the changes in the society caused by migrations, contacts with other people and other habitats, both inside and outside evolutions. For this alone, I'd recommend the book.
It is a bit technical especially at the beginning, and it does use a technical language here and there, but on the whole it's very readable. It touches upon all the more important aspects of this society though its history, and sometime also the less obvious and familiar matters. I'd say you'll find in here all you need to be aware of in regards to Sioux people.
But...
Yes, there is a big `but'.
The author states in the beginning he will raise questions more than give answers, because this is the essence of the researcher. What he wants to do is rouse the reader's curiosity more than quench it.
Although I understand this in theory, in practice, as a reader, I was always left unsatisfied. The author started a lot of very interesting topics, but just when I was getting into the matters - he left me to myself. He never gave a complete information on any topic, nor information that sounded complete, so I always fest a bit cheated. I didn't need to be told `Look, there's a lot of interesting things you don't know, but you can learn' (which is something I already know). I hoped I'd have an opportunity to learn at least some of those things from `this' book.
So, if you're looking for an introduction to the Sioux Nation, this is a good place to start, because it does give you all the basics. If you're looking for something more in depth... this may not be the book for you.