This 3-part BBC adaptation is one of the most faithful novel adaptations I've seen in a while, which I was glad about as Christie's plots are so carefully and intricately thought out that tinkering with them generally makes them less effective. There was a surprisingly star-studded cast considering it was something I'd seen no advertising for (or maybe it's been out there but I just haven't seen any), including Charles Dance, Aidan Turner and Miranda Richardson, as well as Burn Gorman (another, less well-known face from Game of Thrones) and Anna Maxwell Martin.
The scenery of the island was wonderfully bleak and atmospheric, with the intentional contrast of the modern mundanity of the house itself as effective as in the novel. Seeing it all visually for me accentuated the characters' gradual descent into a kind of stress-induced madness, especially, although it might sound odd, in the women. I hadn't really thought about it before, but it seems rare to see middle or upper class women in period dramas in any state other than well-dressed and composed, so seeing the convention of decent dress and presentation gradually break down was very interesting.
In terms of changes, the largest one perhaps was a change from the solution to the murders being a found manuscript in the book to a live confession in the series, which does make sense as being more dramatic and easier to show in visual media. The crimes committed by the 10 guests were also changed for the most part, in a way that made them feel more deliberate and in many cases more violent. My own feeling is that this wasn't strictly necessary, but perhaps it does make the viewer less sorry to see them die as they are more culpable themselves.
Another common alteration to period adaptations that often frustrates me is the addition of sex where it's absent in the book, and this did take place here. I didn't actually mind it, however (and not only because Aidan Turner is very nice to look at), because the characters in question did have a sense of chemistry in the book, and their acting on it in the adaptation served to accentuate the sense of social boundaries and rules breaking down.
I hope I haven't accidentally given spoilers to anyone who doesn't know the story, but I will say it's definitely worth watching, and also reading.