(In the interest of full disclosure: I wrote this before finishing it, because I felt so annoyed. But having now done so, my opinion remains unchanged.)
I liked the conceit of telling Alexander's life using eight "murder suspects" and the narrowing down to who it might have been in the first chapter is done very well, feeling very thought out and using the few historical sources we have very well. Unfortunately afterwards sometimes this careful weighing of the sources feels neglected in favour of the author's agenda and are treated like gospel truth. Using modern crime experts to solve a (suspected) murder committed over 2000 years ago is something I'm also a bit wary of, considering how little we actually know. But that might have been alright and still made for an interesting read, had the author not used the cheapest of detective fiction tricks: he glosses deliberately over important details in order to pull off a "big reveal" as motive for the murderer he ends up with. That's just seems wrong for a book that claims to be historical non-fiction.
Those details? Anything to do with Hephaistion, making me at times rather angry while reading over the glaring omissions. The reveal? That Alexander and Hephaistion were *queue drumrolls* lovers. Um, yeah, that's news to who exactly? Certainly not to anyone who has ever read or watched anything about Alexander EVER.
On an amusing side-note, Roxane as a possible murderess was also mentioned in another quasi-historical Alexander biography - my beloved "The Nature of Alexander" by Mary Renault, who at least never pretends not to be biased. (I am most certainly biased, too - had the cheap plot device not involved Hephaistion, who so often gets short-changed by historians anyway and who I always want to read more of, I might have felt more forgiving.)