The Spanish Civil War is covered in layer upon layer of disinformation, misinformation and just about everything else from every partisan quarter and it is genuinely useful to have to someone as 'English' as Orwell but with a strong commitment to Socialism and some semblance of balance write something as useful.
The book is an editied collection of letters, reviews and other relevant essays from, or surrounding Orwell during his time in Spain, along with a fully revised version of 'Homage to Catalonia.' And when the title says 'Orwell in Spain', it REALLY means it. It collates all the useful stuff from the Complete Works on Spain in one useful reprint that is presented chronologically from Orwell's perspective (i.e. it has letters presented in the time Orwell received them so one from Kopp written in mid-June didn't get to him until mid-July so it presented afterwards). It is well indexed and referenced and is a useful source on the Spanish Civil War from novice to expert alike.
If you are interested in Orwell or the Spanish Civil War or both, this book is very much a must have in every respect. It is well presented and unconfusing, collates everything you could possibly need and is in a readable font (the less said for "The Complete Novels" the better...!), including the witty and personal account of 'Homage to Catalonia' (which makes the main spine of the book). The material runs right up until 1942 with constant reflections and lessons derived from his experience, especially in relation to World War Two in later sections. A well edited and collected book that literally provides you with Orwell in Spain. An essential.