I read Steven Williams' Diocletian and the Roman Recovery in conjunction with Alaric Watson's biography of Aurelian (my review here). Like that book, Diocletian doesn't aim to revise the "standard version" of the emperor's reign so much as pull together the scholarship (as of 1985) about the period ...
I bought this one during my recent trip to the Clinton Presidential Library back in May, but did not get around to it until June. See my note on the book at [http://itinerantlibrarian.blogspot.com/2007/06/booknote-how-to-be-presiden.html]