Not "what makes good espresso" or "how to make good espresso," but "what is good espresso?"
I suppose we'll end up talking about all the usuals: sweetness, acidity, body, structure, look, feel, etc.
Have at it guys!
Well this is going to be opinions, since taste is subjective.
Espresso is semi predictable process. Rarely have I had an "alright" extraction. Its usually good or bad.
Here's a fun thing to do, make a list of 5 thing you don't want to find in an extraction. Then pretend your grading your espresso except every one of those qualities you don't want hurt your score. So start at 100 percent and knock it on unwanted qualities.