RPGMemes

Exactly this.

The game's rules are, mostly, simple, intuitive, consistent, and predictable. In fact, the rules very often seem to follow from the fiction presented at the table! Sometimes, they do it too well, even -- I've seen people complain about Trip being Athletics vs Reflex rather than Acrobatics or Fortitude, but as someone who's taken judo and karate lessons, Athletics vs Reflex is 100% right.

The rules follow the fiction at the table, and that means 9 times out of 10, if you know the fiction being presented, you can just ask for the roll that makes sense to you. No need to look anything up.

The game is also moderately systematized, and functional. That is, a lot of what 5e DMs would just treat as "roll skill against DC" is formalized into an "Action" with a concrete name. These actions act like mathematical or programming functions, in that they can take parameters. So, it's not "Trip", it's "Trip (Athletics)". If your character comes out of left field and does something acrobatic, or even magical, that I think would cause a creature to stumble and fall, then I will leverage "Trip (Acrobatics)" or "Trip (Arcana)", which now makes it an Acrobatics or Arcana roll vs Reflex. This means "Trip (x)" is actually "Roll x vs Reflex. On a success, the target falls prone, on a... etc."

Super flexible, and super intuitive. But formalized, and only presented with the default option, so it looks both complicated and rigid.

I started running the game for 8 year olds, though, and they picked it up very quickly. I do my best to run sessions totally in-fiction, but that honestly gets broken every other turn or so.