Originally written as a boys adventure novel, modern readers will probably consider it more a book for adults.
The plot is fairly straightforward: Our Hero, David Balfour, is tricked out of his rightful inheritance by an evil uncle, shanghaied, shipwrecked, partnered with a historical figure (one Alan Breck Stewart) and caught up in the events of an unsolved historical mystery (the Appin Murder). The body of the novel is a day-by-day description of their flight through the Scottish highlands, on the run from the Redcoat troops searching them out.
Overall, the novel succeeds in creating some degree of tension and suspense, especially in the first half or so, with some classic melodrama elements. The latter half of the novel drags a bit, though, and would probably be less appealing to younger readers and more enjoyable for readers more interested in Stevensons prose style. There is a great deal of Scots dialect, but the most obscure words are footnoted.
Overall, Id recommend this highly to a fan of books like Sir Walter Scotts Waverly or Rob Roy, or to anyone who had a particular love of historical fiction set in the 18th-century scottish highlands.