I'm a BIG fan of the Parasol Protectorate series and have been debating about whether I wanted to give the manga a try. I've read manga based on books and movies before, but have never liked them. I'm glad I finally decided to give Soulless: The Manga a try!
The manga acts almost as a companion book for the novel. It gives lovely visuals of the character and key points of the plot. The cast of Soulless each has their personality shine in the manga and in certain romantic moments, both with Conall and Alexia, and Akeldama and Biffy chemistry can be seen more than in the books. Jokes in the novel are given a second life in the manga. Even though I remember them from the novel the jokes and sarcasm still seem fresh.
However, I would not necessarily recommend this for people who have not read the novel. All you really get is the key moments from the novel without the context or background. The entire manga is just one action or romantic scene after another. While the characters are a little deeper reading this after the novel, reading this alone doesn't do the characters justice.
If you're unsure if you want to read the novel or not, give the manga a try, if you like it READ THE BOOK!