Its tough to say one way or the other on this, because I dont want to say, "yeah, I agree" and look like im running the catch the bandwagon, but I also dont want to disagree just to disagree.
But I will say this...
Ive never been a fan of shots that have a copious amount of crema... those pretty pictures of shots that are 100% crema.. not really want Im after. I do agree with James about being more interested in balance then a "journey" of the cup, however. Over time, I have adjusted my brew pressure to the point where the crema to coffee ratio is where I like it.. Crema about 20-25% of the cup.
And Crema, mottling, flecks.. Doesnt mean you pulled a good shot at all. Some of my best shots Ive ever pulled had waning crema, not even able to cover the whole top of the cup. Granted these were washed centrals and africans, but hey.. Its the espresso Im after, not the crema.
Also.. Bitterness is NOT a bad thing. Lots of bitterness is not enjoyable, but bitterness, in the right amount, can do wonders for lots of things. The trend in America toward bitterness is that if its bitter, its bad. Not true in my book. Anyone who has worked as a bartender(or attends bars a lot
) will tell you, "Bitters" are often added to a drink, and without it, some drinks would not be nearly as good.