Homer's Iliad is well over 2000 years old - and closer to 3000 - and even it wasn't being original when it told the story of Achilles' endeavours in the war between Greece and Troy. Nor is it as though the tale of Helen's flight from Menelaus and the resulting conflict something fiction writers have chosen to ignore until this point (there's been two feature films and a TV miniseries on the subject just whilst Miller was writing the novel). If you're going to jump into such a crowded and longstanding market, you've either got to rejig the basics to the point where they become original again, or you've got to tell the standard story with enough style to make a well-worn path seem new and interesting again.
Miller ultimately fails to do either.
The central conceit to Song of Achilles is that Achilles and Patroclus were not merely close companions, but gay lovers. When asked where she got the idea, Miller says she got it from Plato. I'm sure that's true. But she could also have gotten it from any GCSE student who's been exposed to the Iliad, or even the story of the Trojan War more generally. As twists go, "What if Achilles was shagging Patroclus?" is only slightly less obvious than "What if God was an alien?". Miller was still the first (so far as I know) to actually put the idea into practice, but even so, if your foundations are this obvious, you need to put an awful lot of effort into ensuring the completed structure is pretty enough to disguise its prosaic beginnings.
Song of Achilles just doesn't really manage that. It's prose is pleasingly concise, and the whole book rattles along at a reasonable pace, which is certainly a plus point, but minimalist doesn't necessarily need to feel bloodless and stark, but for too much of the book that's the impression generated.
The novel can be broken down fairly easily into three distinct parts: the meeting and growing closeness of Achilles and Patroclus during peace-time; the build-up to and first few years of the war; and the final days of Patroclus as destiny finally begins to catch up with our heroes. The first two sections call to mind that old saw about writing that is both original and good: the first part is only the former, the second merely the latter. The opening third is all the more frustrating because of the obvious parallels to real life that Miller seems uninterested in exploring. Who among us, in the bloom of puberty and of our first loves, didn't endow the object of our affections with supernatural qualities. When Patroclus looks at Achilles and sees perfection, isn't that what we all did? Exploring what that would mean in a situation in which the one we obsess over actually is as a god?
In Miller's defence, such an approach would require a very different book, one in which Patroclus either is not narrator, or shows a great deal more awareness and agency than he does here. Frankly, those are things he could really do with; there's only so many iterations of "I saw how awesome Achilles was, and thought I was rubbish, then it was time for cheese and olives" you can get through before you long for Hector to show up early and get down to some serious stabbing. There's something very Marty-Sue about Patroclus, constantly thinking he's worthless whilst demigods, centaurs, and the Fates themselves keep alluding to his superiority. A few references to the perverse difficulties inherent in being with someone you consider so much better than you are interesting to digest. Two hundred and fifty pages of it can fuck right off.
The biggest missed opportunity and baffling choice in Patroclus' pre-war adventures involves his time with Achilles in the mountains, under the tutelage of the centaur Chiron. Achilles' mother Thetis , a sea-nymph, has made her dislike of Patroclus very clear, to the point that, unbeknownst to Patroclus, the only reason Achilles doesn't jump his bones when both boys are fourteen is for fear his immortal mother may be watching.
This state of affair lasts for two years after Patroclus first dares a kiss, and is silently rebuffed. Two years in which Patroclus was with his love almost every minute of every day, in which they slept inches apart, in which there was plenty of wrestling practise and long dips in mountain pools and the gods alone know what else. And through all of this, Patroclus doesn't know why Achilles won't kiss him. Mixed messages don't begin to cover it.
A great deal of this will sound familiar to almost everyone. How many of us got hit by our first real, breathtaking crushes (which we called "love" simply because we lacked a frame of reference) when at school, and so ran into those we wanted every day, unable or unwilling to admit our interest, or having already been discovered and desperate to believe that one day the calculus would change and we could get what - who - we wanted? And whilst this might have hit for the first time when the deadline for algebra homework was still a pressing concern, it is a lucky man indeed (or perhaps simply an inexperienced one) who can say they never came across it again.
Miller deals with this ocean of melancholy possibility by writing "two years passed," presumably so she can hurry to the second third of the book, in which the early myths of Achilles are retold in a style which is breezy but entirely perfunctory. But what kind of love story skips the tricky bits? And if Miller didn't come to tell us a love story, then what exactly is she doing here?
The best answer I can find to that question comes during the book's final third which, to be fair, is a great improvement. It is here that once again Patroclus goes through something familiar to us all, the realisation that those we loved as perfect are anything but. What makes Patroclus' awakening so interesting is that it's precisely the aspects of Achilles he loves so much that end up wrecking everything. Achilles' lack of guile and willingness to forgive prove to be evidence not of empathy, but of having so little interest in others that it is difficult to make any impression on him, even a negative one. His all-encompassing quest for immortality through glory seems entirely appropriate to Patroclus when it involves Achilles fighting battles alongside their comrades ("The assembled might of Greece Offended"), but it looks a lot less appealing when it leads to Achilles abandoning innocents to the wrath of Agamemnon so as to paint the latter as a petty tyrant.
In other words, it's about the point where you finally figure out that a relationship is not hermetically sealed; that they cannot be judged simply on internal interactions. Watching Patroclus come to terms with this, and Achilles entirely fail to (indeed it's not even clear he comprehends whats happening) provides a surprising amount of pay-off to what has been for most of its span a fairly lacklustre novel, and does at least give the whole a purpose, albeit a shaky one.
Still, it's a quick read, it ends well, and for those with only a passing familiarity of Achilles, it might work rather better than it did for me. Just don't expect much in the way of surprises, or pretty prose, or any help in understanding how this won the Orange Prize in the first place.
 One of only four women in the whole book who have anything but the briefest of appearances, by the way. She and Deidamia are both deeply unpleasant, and Patroclus' mother is mentally retarded. Only Briseis is particularly sympathetic, and it isn't until the book is more than half done before she shows up.