It is useful to read the Introduction afterwards but not before; Menikoff gives away the endings to Stevenson's tales, which are tales of suspense as any adventure or romance must be. Stevenson's stories take place out in the world of nature, and within the cities and amongst the relationships between people, and inside the psyches, the souls, of the character, although any one story may take place mostly in one realm. The decisions that prompt action are the soul of drama (think of how the musical Les Miz deleted 90% of Victor Hugo's book, leaving only the drama of human moral action). Stevenson is concerned with life, and therefore with death; he sees that it is battlefield of good and evil; and he is one of the few I can think of who describe the journeys of those who have chosen, from what seems to them the most noble reasons, what seems to them the path of the moral high ground.
After I read the book's introduction by Barry Menikoff, which compared Stevenson with Tolstoy, I searched for references to Stevenson in The Essential G. K. Chesterton Collection, which contrasted him favorably with Kipling. I learned that Stevenson was a great reader, strongly influenced by Hawthorne and Whitman, and by the French writers. (I had to stop in the midst of one of his stories located in France and read Monsieur Lecoq.) Stevenson was a craftsman as concerned with the telling of the story as with the story he was telling, and a creator who defined the short story as a genre in both theory and in practice (Menikoff, p. xiv).
Stevenson had an extraordinary vocabulary and was concerned that his readers understand his stories. The result is a rich reading experience that welcomes one in.
I have been watching some movie serials from the 1940's, and am struck by how they too appeal through vigorous action and striking atmosphere, which combine the common human drama with otherness (Westerns in the 1940's serials; Scotland and Hawai'i and France feature in Stevenson).
Thrilling adventure, indeed!