I will start.

I find two things most fascinating about Bridge (among a million other things lol)

(1) The first being the obligatory Duplicate scoring system. It revolutionized the game by getting rid of the luck factor in a card game where hands are dealt randomly. Basically it says "I get a shit hand, and you get the same shit hand. Let's see who deals with it better !"

(2) The other thing that fascinates me is - when the dummy comes down, each of the other three players gets to see about half the deck, but they each have a distinct version of reality in front of them, which drives their individual decision processes. This is a beautiful aspect of Bridge that I haven't seen in other card games.

Would love to hear others' comments on this !