The problem with books on Wagner is that there are so many of them. I agree that Magee's is an excellent introduction. I also like 'Wagner: a case history' by Martin van Amerongen (Dent, 1983). I'd avoid Robert Donnington's 'Wagner's "Ring" and its symbols' (Faber, 2nd ed. 1969). A copy of that has sat mostly untouched on my bookshelves for over forty years, it is one of the most impenetratbly obscure analyses I've ever come across: and these days, is Jung of more than historic interest? Is it still possible to find a Jungian, let alone find anyone to interpret what he says? Well, maybe, but I dont think I'll bother.
Another that I read recently and enjoyed is 'The Wagner clan' by Jonathan Carr (Faber and Faber 2007). Wagner's descendants and their domination of Bayreuth, right up to the present day.
And apologies for repeating myself, I think I've posted the following observation before, probably also in a thread on Wagner. The discussion of Wagner the man and Wagner the artist reminds me of George Orwell's comments on Salvador Dali in his essay 'Benefit of Clergy: Some Notes on Salvador Dali'. Orwell was troubled by the fact that Dali was clearly a skilled and talented artist, and, on the basis of a carefully cultivated public persona, a disgusting person. Orwell noted that the world was split between those who felt that because he was a fine artist he must be allowed objectionable behaviour, and those who felt that because he was an obnoxious person, he could not be a great artist. He says:
"One ought to be able to hold in one's head simultaneously the two facts that Dali is a good draughtsman and a disgusting human being. The one does not invalidate or, in a sense, affect the other."
I think he might have been happy to have that analysis applied to Wagner too.