These were very entertaining books when I read them first at 13/14 y.o., awakening a taste for European history and all that. I wouldn't hesitate to recommend them to teenagers. They could read far worse.

Unlike Dumas, read first in the same years but that I enjoyed re reading a while ago (for all his flaws and so on), I abandonned my re reading of Druon's series not far into the first book. It's like Dallas or Dynasty set in the French middle-ages (and that's made even more obvious when watching one of the two very faithful TV series made out of the books).

His prose is simply academic French (and yes, the man was an authority on the language in his days). Grammar and syntax are flawless and all, his vocabulary precise. But he writes like a French teacher, not a good novelist, and to make it worse he used some fake archaic French (mostly from period referred to as "classical French", so pseudo Dumas, if you wish) that gets very annoying very fast (and of course it has nothing to do whatsoever with medieval French of the time of Philippe Le Bel!).

Dumas's prose was musical, flowing and colourful (for all his occasional blunders, mostly due to the fact all his published books were essentially first drafts and he barely ever reread himself)

Historically speaking, you've been kind to Druon, really. There are historical mistakes, but there's far more details big and small for which Druon decided to go the way of the fanciful historical anecdotes and popular rumors rather than follow serious historians (who would argue, just one example among tons, that this and that person about which there long were rumors of poisoning have not been assassinated at all.. basically destroying most of Druon's lttle machiavellian plot devices). It's not that the books don't teach anything about the period and events to people who don't read much or any history, but it's by and large highly unreliable as an history course because it's in the end mostly fiction set on historical events, or highly fictionalized versions of historical events. The massive popularity of the books is a bit annoying for this, as so many believe they are extremely well researched and follow history closely, and think they know about this period and people now (annoying mostly in conversations with those people, admitedly!). Extensively researched... no doubt, but like Dumas but in a far more pedantic way (Dumas never even tried to pretend his books followed real history closely - rather he claimed he was trying to give his popular readers the spirit of the times he described - as it was seen in his time by people of his political inclination), Druon has chosen to adopt the more colourful inaccurate accounts to build his novels. That'd be entirely forgiveable if these were excellent novels, but for the most part they're highly overrated both about their quality and their entertainment factor.

The seventh book is not really part of the cycle. It's an author/publisher trick to market it as part of it to cash in on the popularity of the previous books (the other books by Druon didn't sell so well as anything labelled Les Rois Maudits), and was originally published apart, after the others.