Well, this is certainly one for the Howard completists. Not that it is only such readers who would be interested in this. It is also great for those who just want to read about another of Howard's characters, those who want a change from Conan, although of all of them Kull is probably the most Conon like. If one ignores the various incomplete fragments and unfinished drafts, most of these stories are top notch, up there with his best work.
These are stories of Kull, of Atlantis, barbarian and savage who usurped the Valusian throne and then found out that holding onto it was a lot harder than taking it in the first place. Aided by a few trusted advisers and his Pictish allies, he endeavours to resist all efforts to unseat him.
Apparently, only three stories featuring Kull were published during Howard's lifetime. A handful of others were found and published in the 60's. All these are collected here, along with the aforementioned incomplete fragments, and arranged in the order that they were written. Throughout, almost on every page, there are hand drawn illustrations to accompany the text and illustrate the story. There's also a good introduction, an informative appendix and notes on the text used in this volume.
I probably wouldn't advise starting with this character if you are new to howard, but if you have liked any of his other work, it is worth giving this one a read.