The Black Company series grew out of a single high concept: What was the daily life of the band of orcs who captured Merry and Pippin in The Lord of the Rings?
I mean, those saps had the ultimate pointy haired boss, no job security, and the world's greatest hero in the world was chasing their butt.
Glen Cook's editor demanded a few changes, of course. The biggest is that the Black Company had to become good guys, had to turn against their evil employer, had to get that all-important audience identification. And a love interest, don't forget we need a love interest. But Glen sucessfully morphed Melkor into the Dominator, Sauron into Lady, and the Nazgul into the Taken, and created a series which transcends the original concept into a study of the horrors of war.
The series gets seriously wierd with Bleak Seasons, the sixth or seventh book (depending on whether you count The Silver Spike). Glen said that Bleak Seasons was delayed several years because after he got the climactic battle scene written, Saddam Hussein went and stole his material. In this book, POV character switches from Croaker to Murgen, the Standardbearer of the Company. Unfortunately for the reader, Murgen is insane. And you don't know whether to trust what he says....
Glen has been accused of leaving dangling plot threads in the final three books. However, a careful reading shows that, by the end of Soldiers Live, we know where the Black Company came from, why they left Khatovar, what the Glittering Plain is and who built it, where the Shadows come from, and who the Shadowmasters are. You just have to keep track of all the alternate dimensions.
One thing never is explained, though -- how come the Limper keeps coming back? Glen said, "Oh, yeah. The Limper is just too fun a character to write about, to leave dead for long."
Based on an interview with the author at Readercon 2000.