The Black Stuff

Does anyone know what it is that makes a good pint of Guinness?
I guess it isn’t difficult to assess a bad pint, but what categorically puts a good one over a mediocre or even average one?
The question’s prompted mainly by my meeting in Dublin on Wednesday – in the cab to the airport my distinguished cow-orker said to the cab driver “There’s nowhere at the airport you can get a good pint of Guinness, is there? Can you drop us somewhere near the airport which does a good pint?” (thereby demonstrating that he’s a man of the people who appreciates cultural nuance, and not just some smug English businessman). The cab driver dropped us at a place a short walk from the airport which apparently the air crews all go to when they knock off, which does a good pint. Two black pints duly arrive, and as promised, they tasted a lot like Guinness does.
The thing is, Guinness tastes like Guinness, and my limited understanding of it is that it’s all chilled & dispensed from nitrokeg, and that when brewed under license it has the same ingredient list (with the exception of Nigerian brewed Guinness, whose grain component is sorghum and which has it’s own distinctive taste).
So assuming the starting materials are the same, the variables you would have are: the nitrogen pressure (assuming that’s the propellant gas), the length of time the kegs been there, the line distance between cellar and tap, the refrigeration temperature, the distance between the tap nozzle and the glass when the pint is poured, the cleanness of the glass, the technique of the pourer, and how often and well the lines are cleaned. Height of the bar above sea level may be a factor too.
I can’t quite put my finger on what makes a pint “good” – I used to think that an easy indicator was the structure that the head made: on a good one you could hold the glass up and tip it by 5 or 10 degrees about a fixed point. The top of the head would remain level, and the “wall” of the head would remain intact, giving the head the appearance of a chunk of icecream.
I imagined that a good pint was slightly more viscous than an average one, although I can’t substantiate that.
I’ve heard anecdotal stories about pub landlords so proud of the quality of their Guinness that they’ve taken pub regulars on trips to Dublin to make comparison, although if what the cab driver said was true then the landlord could have preplanned to take his punters to certain pubs which he’d figured out supported whatever his theory was.
As it was, you couldn’t get a good pint of Guinness at the airport: the bars we saw only sold Murphy’s, another local stout, which I find easily as drinkable as Guinness.
Someone out there MUST have an answer to the question, surely? I’m not going to write on it any further however, as I’m stuck standing in a train vestibule, and this is just making me want a pint.