John,
If I may wade in on this one, it can be safely said that a good (or great) routing must necessarily be based on flexibility, variety and individuality in the nature of the holes in the design.
Flexibility, in this matter, refers to the degree of difficulty experienced in the character of play of sequential holes in that the player does not experience a strong degree of "sameness" and repetition during a round. Few things have a negative impact on the players' psyche equal to several bland par fours repeatedly requiring a drive and a chip or a routing design that virtually dictates a player bottleneck through a series of holes particularly early in the play of a nine hole loop.
Variety closely follows suit in the sense that directionally, well conceived golf course routing design must decree that par threes and par fives should be designed to play to varying points on the compass. Combining this with a broad diversity of length and playing characteristics within the category of par is an exercise in providing a constantly thought provoking process within the individual designer and player while considering sun and wind exposure through the 18 hole round.
The individual nature of holes within the design concept has a capacity to establish identity in the sense that features may be inserted into the routing design to achieve a desired impact in the overall sequence of play.
One of the major processes in the designer's mind will be the thought and consideration of what will be remembered in the play of his particular course, whether from the visual impact or the impressions of the player's compatriots.
The bottom line of the conscientious, talented designer is: "How can I achieve this within a better budget"?