After reading all the histories of Scotland written to cover the higher medieval period, i.e. the 11th, 12th and 13th centuries, I can confidently declare this the best. The reason is size and comprehensiveness. Other studies tend to have little but political or religious-political history. You can read 20 books about Scotland in this period and, while you'll be well versed in Anglo-Scottish relations and the cliches of Normanization, you'll have little understanding of Scottish society. Not so with this book.
Yeah, it has all that stuff, but pages 309 to 519 get into other non-political aspects of the period. The political coverage itself is also good, but keep in mind that Archie Duncan has since published "The Kingship of the Scots, 842-1292" (2002), where he changes his position on several issues. The latter title should be preferred for political narrative, but is expensive. Richard Oram and Dauvit Broun are coming out with new titles soon, and it remains to be seen if these will be superior to Duncan's work or Barrow's "Kingship and Unity".
If you are looking for a title that covers the earlier medieval period, then Duncan's work is less strong. Although Duncan begins in prehistory, the entire period before the 11th century barely receives a hundred pages (out of six hundred), and even that appears to form only a backdrop to Duncan's real area of interest. If you're interested in the earlier middle ages, then see Lesley Alcock's "Kings & Warriors, Craftsmen & Priests", or Sally Foster's "Picts, Gaels and Scots".
You can think what you like about the title "Making of the Kingdom", but you can't deny the book's quality. Anyways, I'd give this book 4 out of 5, but because I know how amazon ratings actually work, I'm giving it 5.