Not bad, not much related to Sherlock Holmes or the Cult of Cthulhu
The graphics are stellar and the cutscenes are great (there is a Remastered version as well now, which I have not seen; I am talking about the original here). The voice acting is not bad (but could have been better). The dialogue is not bad, but also could have been better. There is a nod to Sherlock Holmes's past, as well as a hint of the next game in the series. One thing I especially liked was the way the dialogue gets condensed into a story as things unfold, giving you the option of reading through the sequence of events you have just enacted.
Like a lot of the point-and-click games, you can't proceed unless you have found the needed piece of evidence or answered the appropriate questions. In fact you can't even exit the current area unless you have done these (sometimes it's nice to just wander around and enjoy the spectacular graphics). It was both too hard and too easy at the same time; there was not much call for applying logic but quite a lot of pixel-grubbing (I think the Remastered version addresses this at least; by pressing the spacebar all of the action areas are highlighted).
The Bottom Line
This is a fairly standard point-and-click with excellent graphics and one or two twists. While most of the action is point-and-click, there is one sequence where the clicks are time-limited (you will probably end up replaying this bit quite a few times). There are other challenges where you have to answer a posed question: unfortunately there only ever seems to be one correct answer (which must be spelled correctly) - some latitude or even hints here would have been nice. While I am curious about the improved graphics in the Remastered version, I didn't enjoy this game so much that I want to go through it again.