Confession time: I am not overly enamored of "rules-lite" RPG systems. As long as the system is coherent and well-thought out, I prefer it when the system has rules for all sorts of things - from tactical combat to running chases to social encounters to falling damage and so forth. I like GURPS, I like D&D5E, I like Pathfinder 2E (although I haven't gotten a chance to try it as much as I'd like).
However, one thing that I want to be as simple as possible: NPC/monster creation. When I am the game master, I want to churn out the stats for enemies that the PCs can overcome as quickly as possible. Any time I spend on building NPC stat blocks is time I can't spend on working out fiendish adventure plots.
Here are a few examples of NPC creation in different systems:
Horribad: D&D 3.X, Pathfinder 1E. Too damn many derived values, templates, and so forth. Far too much math for far too little to show for it.
Bad: Exalted 1E/2E. NPCs have all the same stats as PCs, of which there are lots. Plus lots of charms with overly long texts, in the case of Exalted NPCs.
Decent: GURPS, D&D5E. The math isn't too complicated, and you can easily recycle and modify existing stat blocks - though you have to be careful so that these NPCs are balanced in a fight. Exalted 3E edges into this territory with their "Quick Character" concept - but they spoil it with insisting that "significant NPCs" should be built with all the same rules as player characters.
Good: Storypath System, Exalted Essence. I love how they boil down all skills to: "This dice pool is for what the character is good at, this is what the character is okay at, and this dice pool is when they have to do something they have no real competence at" - and the GM can define these however they like, and even improvise this. Then you have a very few other stats like Health and Defense, and you are set apart from a few special qualities! I've started running Scion very recently, and I am very impressed with this.
So, what other examples do you have of RPG systems that do NPC creation well - and which do it badly?
I completely agree on having deep player character options while still keeping things as simple as possible for GMs. From a GM perspective, I love the way some rules-lite games (my preference is for the OSR/NSR style) make it so easy to run a game in that system. But my players, and me when I am a player, aren't very interested in the bare-bones player character options that those systems usually have.
In the system I'm creating, player characters have a skill-point system that they can use to build out their character by purchasing the equivalent of feats to build whatever sort of character they like. It is straightforward, but can get really complex for those players who like to explore those systems.
Meanwhile, NPCs can be represented with 2 stats (Hit Dice and Will Dice), which can be used for HP, morale, skill checks, and saving throws. For combat encounters, you only need to add an attack, and for social encounters or significant NPCs, you can add personality traits and motivations, to facilitate GMing the NPC.
The goal of the system is to marry the player character mechanical diversity that you see in systems like Pathfinder or GURPS with the ease of GMing that you see in the OSR. There's also a sort of "playbook" equivalent which give starting character builds for those players who are more interested in the roleplaying than mechanics, and just want to take something and run with it.