I am not particularly a fan of counterfactual history, but have been reading 'The Armchair General' by John Buckley.
The premise of the book is not so much what if things had happened differently, but more specifically what if allied commanders had made different decisions at various stages during the Second World War. The structure is that for each of eight scenarios the reader is presented with binary options, then for each of those routes there is another binary option and so on, leading to a small number of alternative situations. The author claims these to be 'plausible rather than fantastical' and that seems a reasonable description to me.
The reality is that readers will go back and take all the alternative paths anyway, so it ends up being not so much one counterfactual history as a group of possible outcomes collectively illustrating why and how choices were made. The areas covered are all of a strategic nature with Market Garden being the most operational.
I don't think there are any huge surprises in it, especially for the sort of person who reads wargaming blogs, but it's well put together and I found it an enjoyable read.