You really do discount lord of the rings because of its popularity and its lack of "poetic" writing and focus on characters and plot way to much. It was the first modern fantasy novel and as you say did start a genre. Simply because something is written in flowing prose or rhyme does not make it better.
The french books where the digressions are the point that you seem to enjoy so much...are not popular outside academic circles for a reason.
Pointless ramblings do not a novel make no mater how pretty they be.
Still as one who loves arthur stories I will find this interesting and probably check this out. One question though..Arthur has always been portrayed as the Christian somewhat causing the fall of the celtics at least in the ones I have read (Mort de Arthur for example) is it different here?
Also history behind Geoffrey of Monmouth? Is this where current scholarship says these tales originated? At one point I think they were saying there was actually some king that it was based on..but it was long ago I had time to keep up with scholarship in this area.