here is my criteria for a great espresso:
has to be a boutique italian blend not some mass-produced italian espresso like lilly or worse an American blend from starbucks; cannot be a "pod"--which i have only had bad luck with as a consumer -- but has to be the raw unadulterated bean; semi-automatic machines only --secret, nuovo simonelli is the best!; semi-automatic grinder not more than 8 inches away from machine (guarantees freshness of grounds and proper grind consistency); espresso cup has to be hot before espresso makes contact (again function of the machine); crema on the top has to be golden brown and at least 1/4 inch thick (this is a function of the blend and the machine and the proper grind); complete drip should take about 24 seconds during extraction period (mouse tail)...any less, the espresso will be too weak and any longer the espresso will be too extracted and bitter.
Now you wonder why restaurants in general do not make good espresso. It is pretty involved.