multiple options for every class, not too claustrophobic not too open, clearly defined geometry with good differences in height for each capture point, points being able to pushed/defended reasonably and the map has to have a balance between the classes so that one class isn't overbearingly more powerful than other classes (obviously scout will always be the best but the map can't specifically cater to scouts)

a spire

4 years ago i asked similar questions here:
https://www.teamfortress.tv/28646/
https://www.teamfortress.tv/28714/

What i'm gonna say has probably been said on cirlo's links already

First you have "technical" things :
- good performance
- preferably small file size (cough cough sunshine)
- good and consistent lighting : darkest example could be metalworks, brightest process
- NO INVISIBLE WALLS IN THE SKY REE IF YOU DONT WANT A PLAYER TO GO SOMEWHERE DONT PUT A SPACE OR A LEDGE (COUGH COUGH PHI)

Then you have layout things (5cp) :
- 2 to 3 paths between points
- no useless rooms or hiding areas : look at cp_croissant or bazilion for some bad examples with too many useless paths. Btw , I say that with 6s in mind. Obviously if you make a pub map those additionnal zones are cool
- no 500km long sightlines (cough fastlane)
- offer a good visibility to promote open space fighting : you want to avoid blind corridors where you turn a corner and face the entire team at close range)

Then more opinonated things :
- Each zone must offer one of the 3 fight classes a strength to play around. Ex : badlands spire : scouts already on top of it dominate, demo destroys everything on top of spire from below, soldiers have a lot of blind spots to play corners or get close/bomb
- Holding inside of last spawn should not be good (ex : snipers sniping from spawn and banny binding away)
- Last lobby zone should be made in such a way that pushing out is easy; bad examples include badlands or sunshine where the team holding the 4th cp has a huge positional advantage
- The map should offer options to break the mid/2nd stalemate. For example gullywash makes it easy for people at mid to get players in lower lobby, and sunshine gives good bombing routes to go deep into 2nd, badlands rewards taking control of resupply by allowing players to infiltrate, process lets you have a wide front from sewers to choke, etc.

Some koth specifics :
- Good visibility (very little blind spots on viaduct)
- Simple layout
- Options to flank the defenders ; notice on viaduct how flanking thru the connector/by doing wall jumps is easy, but the enemy team still knows you went behind
- Very wide chokes
- Sniper should not be able to see everything from a safe spot; it's fine to have him deny one or 2 accesses, but not all of them. For example on viaduct a sniper can see everything but cliff by playing on china and on top of house stairs, which is a rotation that takes 2 seconds
- scout must not be able to go anywhere on the CP area without touching the ground
- use flat ground to make soldier stronger(cannery), and displacements/props to make scout stronger (viaduct)

If a high end pc constantly dips below ~120fps on the map on low settings, then it is immediately disqualified as a competitive map imo. Optimization isn't the only factor obviously, but it's really important.

other than fps and shit i really like maps like process or gully where there's always a healthpack up somewhere and not every single part of the map is wide open space, those are the only pet peeves i have about maps

soldier rant

Having pack locations that allow hurt people to get back into team fights faster and not having random geometry or props that break splash (stairs, tables, etc.)

I'm going to have to disagree here. I quite like granary 2nd. Scout doesn't need to be the best class in literally every fight.

honestly for me it was always the mid and the rollouts

moot when winger exists

just keep making process

process is kinda bent tbh

perfectly fine opinion. It's a trade off.
But notice how little badlands or granary are played in pugs/pubs compared to process/snake/gully. To me it could be because there are much more blind spots and as a result a bigger reliance on proper comms makes playing such maps harder/less fun in a laid back environment.
The best of both worlds could be things like the glass panel on gully last, or on reckoner. Gives you good visibility, but one that wants to see what's on the other side still has to expose to a flank

Also with gran 2nd and blind corners as a soldier you experience the dumbest shit in this game when you face a scout, direct him, do as much damage to yourself as you did to him, and die to one scattergun shot

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a map needs to emphasize something about a team's skill.
Process emphasizes individual DM, team DM(synergy), and the ability to manage momentum(knowing how far to carry your momentum and how to stop a roll), making it the perfect pug map.
Granary and Badlands, for example, had a role in emphasizing tight teamplay and in general had value in requiring a team to know precisely when, where, how, and why to take fights, meaning their value as pug maps is nearly nonexistent, but they were great ways to stress a team in ways that exist far less in other maps, probably because the skills that allow a team to dominate Granary and Badlands aren't glorified in the way the skills required to dominate Process are, for example.
Gullywash does a good job of highlighting your splash classes without actually leaving scouts behind by letting you bomb to/from anywhere and having reasonable high ground without such insane high ground that scouts can be made irrelevant.
All of the long-term 6s map pool has some sort of actual purpose in enabling different types of play.

As an example of a map that is hated and for good reason, Clearcut exists to constrain a team and is a painful slog of a map because of it. The left side of the map exists to be a death zone, constrain the speed of a soldier's rollout, and to arbitrarily prevent players from pushing out of or into that portion of the map. The right side of the map exists to be a giant spam corridor which is also arbitrarily segmented off by an invisible wall blocking you from high bombing into the back portion of the map, for example. I'm sure other class-main player would be able to explain how the map constrains them, but I've at least provided what I saw a soldier.(iirc our scouts were complaining about point being a low ground death hellscape and being permanently on shed duty because there is no other option than to watch the only two bombs on the entire mid and our demoman had to essentially afk holding m1 looking at sheds 24/7)

And as an example of a map that people find hard to accept, likely due to its redundancy, Propaganda. Propaganda is basically Process 2, electric boogaloo. Mid can be turned around by any class given they play out of their fucking minds and it is about equally possible to get rolled to last equally fast. I would say I like the soldier routes on Propaganda more and the pushes into and out of last are more interesting than on Process and that the second is generally more scrappy, but it still doesn't really fit an entirely unique role and the skills required to dominate Propaganda are nearly the same as the ones required to dominate Process, so it's hard to accept a map so redundant. Personally, I like Propaganda and understand why a lot of people thoroughly feel no need to waste our collective time with the map, and don't see why it exists in the same map pool as Process.

And there are things that break maps regardless of what potential exists.
Badlands mid is known specifically for being a hellscape made specifically for the purpose of torturing the souls of anyone who believes a splash weapon should function and Spire is nearly as bad. Its last also caps too fast.
Propaganda b16 crashes half of at least one team connection almost every time I have ever played it, has performance issues, and also was incredibly visually buggy on some computers(like not being able to see through thresholds, for example) on older versions.
Clearcut has intermittent performance issues.
Granary 2nd has a bunch of dumb bullshit in spite of the main arena of the point itself actually being an interesting use of thresholds. Lunchbox exists. Why?