I've recently been watching
Shetland on iPlayer. It's a pretty good crime series set on Shetland. After a bit of a wait, I got
Raven Black, the first of the books on which the series is based, from the library.
It's not the first novel to be adapted (they did
Red Bones, the third book, first), so it's possible some of the changes relate to events that will happen later in book-canon, but I was quite surprised at how different the book and TV were. The main plot is quite similar (in terms of who killed whom and why), but there are changes even then (Magnus Bain's involvement in historic events, particularly), but there are number of quite significant changes to characters - Tosh doesn't appear at all, and book-Cassie is a young girl still living with her mother, whilst Perez is significantly less sympathetic (in particular around his opinions on Sandy). And the solution in the book seems quite rabbit-from-a-hat, even when I knew who the killer was in advance.
I am undecided if I want to try and read more of the books by Ann Cleeves, but it was certainly interesting to read
Raven Black (and unusual for me to be coming to the book-canon second rather than first).
ETA: There's a short film
Alison O'Donnell Remembers: Shetland where the actor who plays Tosh talks about how and why the character was developed for the TV adaptation.