On the subject of medieval French, I can say that it is fun to read (or rather, decipher). I bought the Pleiade two-volume anthology of French poetry and also Tristan et Yseut and the Chretien de Troyes volume, and it's all fascinating. The Latinisms, the places where the language looks Spanish or Italian, the "missing" letters of later French noted by the circumflex accent are there...it's the sort of thing that someone who likes languages can really appreciate.

I think that I will stick to Dumas and other classical writers for reading "historical fiction" in French - even though I know that he warps history, it's likely to be written better and provide a more pleasant reading experience.

The Druon series was very, very easy to read and I was able to finish a book fairly quickly, so I stuck with it to see how he presented later events (except, of course, the seventh book, which was bad even by Druon's standards).