Man this question is depressing.

I'm looking through steam, and I can't think of a single noteworthy mechanic in any of the recent AAA games in my library. All of them are just the normal industry trends to various levels of polish. But then there are indie games:

Noita (action roguelike)
The game world is a gigantic Powder Toy full of secrets, and your offensive wands are insanely customizable with lots of interactions. The huge array of choices and focus on preparation makes it the only action game I've played that gives me the same feeling as Nethack.

Everspace (space sim rogue-lite)
The story integration over multiple permadeath runs is neat, and after your first win, it gives you extra goals and an actual in-game reason to do more runs.

From the Depths (naval construction thingy? Like Kerbal but battleships)
Just the absolute dedication to complexity as a goal. Weapons are made of multiple blocks, so you have to build a ship big enough to hold the size of weapon you want, and then you have to decide how to build the gun.

Indie games can get away with taking one mechanic and making that the game, I guess. AAA not so much.