I'm thinking of picking up Immerman's CIA in Guatemala: The Foreign Policy of Intervention, but considering that it was published in 1982, I'm wondering if there's any more modern works on the subject just due to the fact that more information may have come out about the CIA's involvement since the publication of his novel.
http://www.worldcat.org/title/denegado-en-su-totalidad-documentos-estadounidenses-liberados/oclc/48653487 thus book, only available in Spanish and difficult to find, is very worthwhile, it is full of released CIA documents which are in English and additional text in spanish
I'm not a specialist for Guatemala, but found Greg Grandin's "The last colonial massacre" very good. It takes Guatemala as an example to look at US/CIA influence in Latin America more generally - you could probably find other good works in its bibliography. Grandin has written a lot about Guatemala, so might see if other books of his like the Blood of Guatemala are more interesting for you. I should note that those are quite in-depth.
Also this is not a book, but Pamela Yates has made a trilogy of documentaries on the civil war - eg When the Mountains Tremble has some great and very sad historical footage, it's probably the most biased of the 3 though.
Nick Cullather's Secret History: The CIA's Classified Account of Its Operations in Guatemala, 1952-1954 (1999) is a standard book on the topic, alongside Immerman's book. They're older but they still check out.