Attempting a one-volume history of anything that has existed for over 2000 years is no small task. Now try to keep it "brief". Once again Modern Library deserves praise just for tackling the task. Martin Marty's emphasis is on the spiritual side of the Christianity in The Christian World, with the institutions taking a back seat. His scope is larger, geographically, than Paul Johnson's admirable yet European-centric The History of Christianity. You won't find a tremendous amount of information about individual churches or creeds but you will meet an interesting array of characters like Origen who decides to go the extra mile in curbing his instincts by castrating himself. (Whether or not this was entirely a DIY endeavor or not isn't clear from the text.)
With material like this the early part of the book glides along. Marty has an eye for a good vignette and a good quote, like the nun who responds to a monk who averts his gaze when he sees a group a nuns. "If you had been a perfect monk, you would not have looked so closely as to perceive that we are women." I do believe that's the early Church equivalent of "in your face, holy boy." Then things bog down a bit and Marty seems to lose a bit of his spark, churning out lines like "It was unholy Christian holy war". Now really. For one thing, what "holy war" isn't unholy? This is just the start of a catalog of atrocities committed by men and women allegedly to act in the name of a religion. This is hardly a newsflash. On the other hand, this occasional heavy-handedness seems to me to be the result of trying to tell all sides of the story in a limited space rather than axe grinding.
All in all this is a solid effort, more history of Christianity as a faith rather than a historical force. It didn't leave me wanting to read more nor did I feel like I have the topic well-covered now but I did learn a few things and what more can one ask of a "concise" history?