Fit and obsessive attention to detail. If you handle a high end factory gun like your TRP, a semi-custom gun like a Brown or Baer, and a true hand built custom, you'll notice that at each level the fit gets a little tighter, the components are a little higher quality, and you will find more hand work. Its like comparing a pair of custom made boots to a similar pair off the rack. They may both be fine boots, but the custom pair will be more finely fit to your specific foot and needs, and will have finer detail work.
I have to disagree and say that those come under "personal taste/ specific requirements" The tightly fit hand built guns are far more prone to stoppages and ammo sensitivity than guns built to less demanding tolerances.
The 1911 was never intended to be a "GREAT" gun, it was designed to deliver a whollop with combat accuracy every time the trigger is pulled on a loaded chamber. A $400 pistol that rattles but does that is FAR greater than $2500 dollar fitted slide pistol that only likes 1 or 2 brands of ammo and jams on crud after 50 rounds.
The type of shooting YOU do may require that type of fit, your budget may support having a particular pistol that is a beautiful safe queen until you need to make one certain type of shot.
Most of us are not in that position we are looking for a pistol that will do ALL potential pistol chores in an acceptable manner. That means only things (This applies to any platform Semi, Revolver, Polymer etc. ) It has to provide the reliability of the sun rising in the east, It has to give decent "COMBAT ACCURACY" say all shots in 3 inches at 10 yards, a pie plate at 25.
It has to be with in your means, if you can't afford it then the rest doesn't matter because you won't have it. The last one is adaptability.
Any thing after that is entirely dependent on YOU, what kind of stocks are you comfortable with, what sights are easier for you to see. I don't like ambidextrous controls, you might be a lefty, I carry mine for personal defense and recreational blasting, you may lock yours in the safe until the next bullseye match.
What makes the 1911 a GREAT pistol is that it fills all 4 of those criteria.