Hi!
I consider CTF to be my favorite gamemode, and I mostly understand how it works in tons of different games, and what makes it one of the worse gamemodes in TF2.
CTF doesn't work like any of the other gamemodes in TF2. Like, at all. Chokepoints and flanks that would make the best KotH map in the could would make the worst CTF map in the world for the same reasons that make them great in KotH, and no other gamemode is quite like CTF in that regard. Sure, payload and arena put the focus on different parts of areas, but with CTF, it's not about areas at all -- except *maybe* the intel room.
I feel like what trotim says about routes being too small and there being too many is justified, but I feel like it's not as bad as I feel like he's saying it is. Having tons of equal routes on a CTF map is actually a good thing, as long as none of them are overpowered like that one on doublecross and they're not all terrible like the ones on 2fort. And, I don't feel like there's anything wrong with having really skinny byflanks if they're not too long and not too many.
I counted about two major and one minor route in a given base, and that's great! The problem is there are so many byflanks and you can't really tell which ones are byflanks -- it makes the map feel "spongy". There's nothing wrong with a spongy map in CTF like there is in push CP, but it can't feel spongy, because it only confuses the player. Also, a lot of your minor hallways are really long. Like, junction long. Like, meandering like the lines in the letter G, but ultimately going in a 300-500 unit straight line long. It would be a great idea to shorten some of them and pop out the rooms next to them, but I don't really have any concrete ideas where to do that.
There's nothing wrong with having small rooms where connectors connect to eachother in a CTF map. That said, it would be a lot better if you picked a couple, but not all of the, main routes into the base so that classes that rely on open spaces would have a place inside the base to have fun. The main, primary route into the intel should be nice and big and fat and have interesting geometry that can fit tons of players. The area between doublecross's spawn and bridge is a great example (even if I don't at all ilke the fact that the spawn is right there at all)
Also, your vent's bottom should slope up earlier than it does. You'll have to pull the back's slope earlier too of course.
When people make the misconception that CTF maps are fine with the same style of flanks and chokes as cp or pl maps, bad things happen. Even if it's TF2, the nature of the gamemode object being a thing that moves so rapidly through any part of the level makes zoning function differently on a fundamental level. You can't put the gamemode object in a place where it functions well and build an area around it. I mean, you totally can, and you might get somewhere like that, but you need to think about the ways that connectors work so differently too.
There's a GG2 map with a tower in the center that functions as a chokepoint so strong that it's basically a KotH map with a skill-based timer. It's like turbine, but orders of magnitude worse. Turbine is tolerable. Maybe half way to being untolerable. But on turbine, the CTF part of the gamemode still happens somewhat normally. On the map I mentioned, the mid advantage defines whether you can get the intel or whether you can defend with near perfect accuracy.
It's not about connectors where people block them off against pushes unless the push is an uber, or that people use to jump on other people from the side. It's about routes that people can take in and out of the base to avoid conflict, what kind of conflict they're going to run into, people being forced to take longer routes because of all of that and being cut off from the connector from another route.
The turbine re-artpass is great, it's amazing, and it's all because they added a bypass from one of the routes to another one of the routes. Instead of having these two connectors that connect together like an H, it has three connectors that connect together like an A with an extra line down the middle, and the connector that's most useful for rotating into the other connectors is the connector that's the least useful for doing anything else. It fixes the problem that TF2's had with CTF ever since it was released, and that is that a vast majority of classes are too slow to cut off other classes with brute force -- they need geometric, tactical, whatever you want to call it in this case advantages.
The reason I'm going on ranting like this is because you have all the concepts there -- minor connectors between major routes, few explicit chokepoints -- but things don't really add up. The easiest to find and widest connector into the intel does a little zigzagging in boring hallways, then ends up right above the intel with a height advantage against players and a distance advantage against sentries. By all means, you should totally be able to walk in the front door, kill everything, take the intel, and leave, but the people in the other parts of the base should be able to cut you off when you leave, too. I don't see any byflanks from the other routes into the main route, and it comes out by far the shortest of all the routes. If you make it have better rooms along its hallways, and make it meander a little more meaningfully, and pull back where it comes out outside, and make the other routes shorter but not too much less cramped, it would be great.
I think I'm procrastinating.