Since I love the anime a lot and I was dying once to know more about manga, now that I received it I would like to share it with every other fan that loves this series as much as I do.
Personally, I absolutely love it. The art is pretty. It is not professional like e.g. CLAMP Im a big fan of, but it has a very gentle, shoujo feeling.
About the plot. Reading manga is like watching anime with skipping only to episodes that contain at least a little bit of Francis or Black Rose or any other crucial scenes. In other words, its as if someone took out the best of the story with some needed modifications in order to make it shorter.
The differences - Its true that some characters are cut out, but to tell the truth, Id call it the other way - the ones that are 'missing' in the manga are the type of characters they add to anime to make more episodes of the series. That there is indeed no Mary Anne and Rosemary doesnt turn evil was a great relief to me. In manga there is Nadja, everyone from Applefield and Dandelion troupe (Kennosuke is here from the beginning), Francis, Black Rose, Harvey and TJ, Christian, Leonardo and Thierry, Oscar, Raphael, Rosso and Bianco, Herman the bad guy and of course Nadja's mother Colette and Duke Preminger.
I dont think you can say they cut out Keith. Its only that his true name is not mentioned and the plot around him and Nadja revolves other way than in anime; he just remains Balck Rose and there are certainly fewer scenes of him without Black Rose's costume. This is where Im really happy I read the manga - for the biggest difference would be the way Nadja finds out about Black Rose and Francis and how she feels about them later - its completely different.
Keith/Black Rose does return Nadja's brooch in manga, for example, but its also different. All Black Rose scenes from anime are included, the masquerade ball, Venice, etc.
The ending is a little different, but its a beautiful ending.
Id recommend this manga to all shoujo/romance lovers and Nadja fans.
I uploaded some scans on minitokyo, in case someone is interested in art style (cover doesnt tell much thats why)