These stories improve as you go, til the last few are very well put together indeed. Like the better Holmes pastiches, they're a mix of real historical events, "borrowed" fictitious elements (like the dead ship from Dracula) and pure invention. I get the impression that there was no intention initially of an ongoing narrative, as the progression from one story to the next is very uneven at first. And the stories themselves are pretty uneven, though they seemed to me to improve markedly around the third or fourth story, when Holmes and Watson make their appearance on the scene.
So far as the Holmes element goes - it was refreshing to see someone give Watson a turn in the spotlight, particularly a Watson bold, loyal and resolute, as Doyle surely intended him. The Holmes we meet in a couple of these stories, however, is a boorish stranger and while the stories are imaginative and the adherence to canonical dates and facts is impressive, I disliked McGregor's characterization of the retired detective.
That aside, these are worth reading and more enjoyable yet if you read the author's note for each story.