I got into this comic at the suggestion of a comic shop owner here in Houston. I had seen it sitting on the rack, and when I went to purchase the comics I had come for (Preacher I think?) he started telling me about it, and I had to check it out. From then on, I was there to pick up every issue.
Essentially, there is a government program that trains people with Dissociative Identity Disorder (Multiple Personalities) to carry out assassinations and other top secret missions relying on the abilities of each of their identities. Each one has three, save for Duncan who appears to have a distinct 4th, and the catch is that each one of them represents some profession, such as the titular Cowboy Ninja and Viking. And there's not just one of these guys. There's like 15, each with their own set of skills (like the hilarious Davy Crockett, Marine, Chili's Waiter who wears a racoon skin cap and 'flare').
The ending to the first story arc isn't entirely satisfactory, but the story as a whole is ridiculously awesome and has some of the most hilarious dialogue (not to mention best artwork) I've read in some time.
Also, I ended up getting this TPB after I lent the comics to a friend, and I can tell you it has all the cover art included, as well as keeps the original coloring in tact. That is to say, it's black and white, with a different color used for accenting in each issue.