Well where to begin. There appears to be a lot of these being worked on at the moment, and whilst they flex and change to meet each individual projects requirements do we really have a handle on what fundamentally makes a good customer journey map.

Well I think that service design tools has a really good definition, but not too many good examples. Which probably shows that not too much design thinking has gone into this form of diagram. So they say
“The customer journey map is an oriented graph that describes the journey of a user by representing the different touch points that characterize his interaction with the service. In this kind of visualization, the interaction is described step by step as in the classical blueprint, but there is a stronger emphasis on some aspects as the flux of information and the physical devices involved. At the same time there is a higher level of synthesis than in the blueprint: the representation is simplified trough the loss of the redundant information and of the deepest details.”
It also include a useful link to those nice folks at engine who explain why it works for them. Adaptive Path also have their take on this, and how the information should be structured in their post The Anatomy of an Experience Map (which isn’t quite a customer journey) but I like the way they divide the information up.
a) A framework. I have only recently started hearing people refer to this as a framework, but it appears to be the underlying grid or table on which the journey is plotted. The vertical axis contains channels which relate to the medium of the experience, books, papers, TV, internet, mobile. So a spectrum from analogue to digital. The horizontal axis represents stages of the journey, so from beginning to end. This is often described in an experience based way (discovery, research, action, reward etc) as opposed to a time based way ( 9am to 6pm etc).
b) Key moments are plotted onto this framework. So if the customer journey is booking a holiday it may start with a research stage using the internet channel.
c) Key moments are annotated with evidence that supports them. Seren accompanies the key moments with a note which can be a quote from the research, or a more detailed description of the moment. In design terms this is often a problem as it is difficult to fit the text to the touch points without the diagram becoming cluttered.
d) Emotional feedback. The client will often want to be able to see at what stages in the journey their are good touch points and bad touch points (pain points). This requires the addition of a graphic motif to represent this. Sometimes its as simple as red for stop (pain/alert) and green for go (good/carry on). But often the designer needs to express complex emotions, bored, frustrated, happy, sad, and resorts to a range of pictograms or colour coding. This is another level of information to fit on the map, and so should be handled carefully. Personally I don’t think sprinkling smiley faces over a map/chart/diagram has ever helped it.