What game mechanics do you enjoy or that surprised you when playing a game? I recently started playing Tunic and I love building out the "manual" for the game and getting hints on how to play.
Titanfall 2 was so good, I miss it. A lot of it's slick movement mechanics show up in some of those modern "movement shooters" like Ultrakill for example.
Double jumping. Something about double jumping just always feels really liberating. It's such a strange concept as well, with no analogue in the real world.
Creative allowance. Even if it makes the game "unbalanced".
Just Cause 2 with the grappling hook you could attach one end to a statue and one to a truck.
Grand Theft Auto 3 was the first game where I realized I could complete an assassination by stealing a police car, use the swarm of police cars following me as a "net" to trap my target's car so he couldn't drive away, and then blowing up the pile of cars with a grenade.
Rimworld where I can create a settlement of nudist vampires trading beautiful wooden sculptures for slaves to feed on.
The Sims 3 of course.
From the Depths, Minecraft, Space Engineers, Valheim also to a large degree.