2.5 stars. This is an amazingly frustrating book; it has so much potential, and for the most part wastes it.
Problem 1 is the genre itself; this is yet another "fractured fairy tale" a la Wicked, in this case doing the alternate take thing on Camelot (in the form of a journal from a slave girl who happens to get caught up in the palace intrigue). Now I'm admittedly not a huge fan of that gimmick, but books like this are the reason why--half the time, it seems to think that the entire point of an exercise like this is just to flip every character and plot point around and then wait for you to fall over laughing at how clever it is. Arthur is bumbling and feckless, Lancelot is a drunken womanizer, Guinevere is a ball busting tomboy, and Merlin is just a clever non-magician who understands people; therefore, we should be entertained because IT'S TAKING A FAMOUS STORY AND TELLING US THE OPPOSITE. Hah! Comedy gold, people, especially when it is so clumsy that you feel like you are constantly being reminded that you are reading a story, rather than being allowed to immerse yourself in it.
(Problem 1.5: it also falls prey to the genre trap of trying to "cleverly" work in details from the original in ways that have no relevance to the story other than to show us how clever the author is. Eg Excalibur didn't come from the Lady in the Lake; it came from Lancelot (du Lac)'s wife, the lady du Lac. Again, hah! This is high comedy.)
Problem 2 (and the largest part of why it is so frustrating) is that the other half of the time, it actually tries to break free of that framework, occasionally giving characters some depth and complexity--only to take it away again whenever an actual three-dimensional character would get in the way of the gimmick. For example, Lancelot, we learn, is angry that Arthur ends up with Excalibur, which was supposed to go to him when he married his wife--but for reasons that are never fully explained, he suddenly becomes Arthur's right hand right when him being a pain is no longer convenient. There are tons of moments and characterizations that, if the author had just written a book about a slave girl's journal about palace intrigue, would actually have led to a really enjoyable book. But every time there's a threat that the tale might get interesting, he has to reign everything in for the gimmick--and once again, the reader is pulled out of what should be a good tale.
Problem 3 is the framing devices, of which there are many and none of which really work. First we get the cover, which has nothing to do with the book--where the former makes it seem like The Camelot Papers refers to some tabloid paper of the era, instead, as noted above, it's actually just a journal. But rather than just present the journal, there's a completely jarring "academic" preface about the recent discovery of this journal, which in no way affects the story or how it is read, and only serves to remind the reader of the artifice of what is going on. Then the journal itself begins--but rather than do a more traditional epistolary style, the author starts each chapter in the first-person present, as if the narrator were in fact writing in a journal in real time, and then slides into regular first-person past narration, and then occasionally breaks back to first-person present, all again to no effect other than to pull the reader out of the story.
And Problem 4: the author tries to set up a mystery or two native to this tale alone, but then in many cases leaves such glaring clues that there is no mystery, and in the other cases, throws out deliberate and unaddressed red herrings that, once you realize that they were just there to mislead you and that they will never be addressed, again pull the reader out of the story. (e.g. If you want to have a scene where someone is poisoned and the narrator notices someone smiling as it happens, have the narrator notice lots of details, of which that is one, rather than just throwing out the sole observation that person X smirked as person Y downed his drink and fell over dead--but if you ARE going to just throw that one observation out as a red herring (because person X had nothing to do with the murder), you also have to at some point explain why person X smirked, or you're just jerking the reader around.)
This was far more than a piece of fluff like this deserved, but it was so close to actually being worth reading...