I think it's fair to say that 100 people asked this question are likely to give 100 different answers.

Many are answering with things they don't like about indisputable luxury hotels.

I think a luxury hotel by most accounts will:

(1) be beautiful/appealing to the eye (beauty is in the eye of the beholder), certainly with respect to interior and often with respect to the exterior or surroundings/views

(2) offer very good, more personalized service (again, this is in the eye of the beholder)

(3) usually be in desirable locations (again, eye of the beholder)

(4) offer nicely appointed rooms in a tasteful or spectacular fashion (again, eye of the beholder)

(5) have more services/amenities than your typical hotel

(6) nowadays, likely have a very nice spa facility (which matters not at all to me)

(7) have very good food/dining option(s)

(8) attempt to deal with mistakes/problems with more concern and polish and be more likely to arrive at a resolution (but with no guarantees)

(9) be followed with a higher than average price point, reflecting the better than average service/amenities relative to the local price point

Some luxury hotels are "more luxurious" than others, usually because they do or have one or more of the above better or more than others.