Having read all the stories, this collection contains everything you need to enjoy Sir Arthur Conan Doyle's works. Points to mention are:
There are only 4 full length books - A Study in Scarlet, The Sign of Four, The Hound of the Baskervilles and The Valley of Fear. The rest are short stories. How infrequently Professor Moriarty or Holmes brother Mycroft appear in the original stories. The Tales of Terror and Mystery don't contain Sherlock Holmes, but are all well written and worth reading. The short stories are understandably short, so don't leave much room for many twists and turns. Although well reasoned, Holmes pretty well always gets it right first time. There is a lot of variety of characters and stories. It never felt like I was reading the same story twice.
The free sample gives you all of the first novel, and nearly all of the second. This collection is a worthwhile buy that has clearly stood the test of time.