Comments

Alright, here's some feedback:

In general:

• The brushwork and detailing is very, very nice indeed - maximalist, but not too crazy, and pretty consistent throughout.
• Good use of inaccessible areas, they really help achieve that classic Half-Life illusion where places seem like a part of a bigger world.
• Sequences are very well executed (that scientist with the gun startled me as much as I startled him, lol), and the use of sentences is spot on.
• Most of the map is pretty silent, could use some more ambient noises (especially in larger areas)
• There aren't many enemies or weapons - if it were an intro map in a campaign that would be fine, but since it's a single level it feels a bit lacking.

Specific issues I found:

• These types of light brushes are too solid-looking, a lower FX Amount (renderamt) value would make them more transparent.

• The pushable cart in the beginning can be used to climb past the crates blocking the corridor, but there is no way to get back from there.

• There's a null face in the room with the barney and scientist that is visible from the vent (if you look hard enough).

• The player can jump down this rusty shaft and get stuck.

• I'd recommend placing the crowbar around here instead of later, to encourage the player to break this window.

• This whole area down here is a bit too dark, the ladder is barely visible.

• A foolish player can wedge himself between the large elevator and the light on the wall, a clip brush is needed here.

Overall it's a very nice level. The ending's pretty abrupt, but that's to be expected from a single standalone map. I'd like to see it make a return as part of a larger campaign.

Yes, apparently Valve chose to split t0a0b into t0a0b1 and t0a0b2, but forgot to remove the original. There is a level transition from t0a0b back to t0a0a, but it's broken. However, turns out it's possible to go from t0a0c to t0a0b by swimming back towards the underwater gate right before the HEV charger section. Whether this means the rats in t0a0b should be counted as well or not, I have no idea. Same goes for the ones in the Blue Shift, Dreamcast port and PS2 port iterations of the Hazard Course.

Who knew chasing rats would lead down a rabbit hole?

Yeah, the rats weren't news to me either, but that particular rat above the hologram took me completely by surprise. The OverWiki says rats only exist in Hazard Course but doesn't say how many. The Fandom Wiki says there's four, and "none have been found elsewhere"...! I just think it's weird this one inconsequential detail has escaped the very wikis dedicated to documenting these inconsequential details.

Also, Drug Barons seems interesting, I'll check it out. Thanks!

So I've been using both editors more-or-less simultaneously for a little while now, here are some things I find worth mentioning:

• TB works with .map files, J.A.C.K. also works with .map files but saves them as .jmf files. Going from J.A.C.K. to TB means exporting the .map file in J.A.C.K. first.
• TrenchBroom's groups do not carry over to J.A.C.K., nor do J.A.C.K.'s visgroups carry over to TrenchBroom. To keep brushes together between editors, they have to be tied to a brush entity like func_group.
• Unlike J.A.C.K., you can't have more than one map open at the same time in TB, so copy-pasting things between maps requires you to keep opening and closing them. This makes using a separate map as a "prefab stash" possible, but annoying.
• For the reasons above (and probably a lot more) switching back and forth between editors on the same map is likely a bad idea.

Excellent example! I hope we'll see more fully-functional elevators in maps from now on. Soon we'll have Elevator Action remade in Goldsrc! Seriously though, this is very neat.

Also, this reminds me of an essay I've watched recently about the many ways elevators are used in video games, it's a good watch.

Played again on Hard, its a lot better now!
Here is some more feedback:

• There are no autosaves! it's a good idea to place them before fights or dangerous areas, or the player will have to start all over again if he forgets to save
• The player can get stuck if he jumps on the chair in the starting room
• First fight is much more fair, good work there
• Office corridor fight is better, but I liked the old pushable crate, maybe you could create another similar area later on where you have to push a crate to avoid getting shot, I just think that's a nice idea
• Jumping on the large crate in the green goop room is possible, but too difficult, might be a good idea to add another floating crate next to it
• In the corridor behind the switch that lowers the goop, the door behind the zombie opens if touched (it should be a fake door)

Very minor details:

• The toilet stalls don't have toilets in them
• The hand dryer sound plays forever if you press its button, it should ideally play for a few seconds then turn off, every time the button is pressed
• I recommend using a trigger_endsection to send the player to the main menu when reaching the end

You're doing well, the gamplay here is fun! Keep going!

Edit: I looked at the sources and there's a few more things:

• The info_landmark entities should be in the exact same spot relative to the map
  In the first map
  In the second map
• In the first map, there is a window on the outside that matches the wall right over the sofa in the corridor fight, but inside, the wall has no windows
  The wall in question... Wait, how did that grafitti get there?
  In the editor, the front door and the window lead nowhere

These two points fit my own experience to a T. I've tried making sketches and blockouts before, but none of that helped me design an environment for a map. The sketches didn't go anywhere because I found it annoying to represent a 3d environment in 2d paper (when that was not the point) and the blockouts did little to get me to think of the finer details - and sometimes I'd just stare at the editor, panning the camera view around without any idea what to change next.

For months now I've been trying to make a small campaign, maybe just a single map in size, that I can release and get feedback on to better grasp HL level design before starting to make full-on mods with assets and code and whatnot. I didn't really have a clear goal other than that, so the map keeps changing and changing - it's still a blockout almost entirely made of grid textures - but it's beginning to settle into a defined shape now. I think what made me stick with this particular blockout is that, for all the others, I was trying to either create an entire environment I could "populate" with gameplay later, or build a level around a single central setpiece; but for this one, I tried to make the map complement the gameplay, and that spurred me on to keep adding to it, despite the fact that even the basic layout was still far from clear. Urby is right, blockouts shine when you want to know if what you're doing is fun.

Just like yourself, I want to make maps that make realistic sense, but I feel like I'm becoming more lenient on that front now. After revisiting Valve's maps and playing a bunch of mods to see what I could learn from them, I started to think the map design of classic HL isn't really much less abstract than good ol' Quake, in the "feeling like a real place" sense. And I kinda like that slightly liminal vibe anyway, so now I'm focusing more on making a place that is fun to traverse and fight in, though the realism is still an important factor that determines what kind of place the map will be. For example, I decided to make this map end with the player riding one of those big diagonal elevators up into the darkness, so to make sense, the map will be a deep underground storage area like the one at the start of the Lambda Core chapter. Building it ended up becoming a bit of a cycle where sometimes the gameplay informs what the map will have, and then what the map has determines what kind gameplay fits best, so it's all starting to converge into a clearer picture now.

About Trenchbroom, I actually learned to use it a bit (but didn't make any finished maps) and I can confirm it really is better for translating that 3d space you see in your head into the screen. It can be faster too, when you get used to it and learn the shortcuts - I recommend Markie's tutorials for these. I never tried to use it for Half-Life though, I'll have to see if exporting to J.A.C.K. works smoothly or not.

Oh, and, about ADHD: I've already asked my mom multiple times if I was ever diagnosed with it as a kid, but can't seem to ever remember what she said. Maybe it's because, by the time she answered, I already stopped paying attention...

I like these maps, even though they start very hard and then get easier - it should be the other way around!
I played it on Normal difficulty, and the first battle with the grunts is still way too punishing. Cover is necessary to fight all those soldiers, but the cover becomes a death trap almost immediately when the grenades start to fly. The GL grenades were the worst - they can kill almost without warning because they explode on contact, unlike the hand grenades which give the player time to escape. A fight like that would feel more adequate as a conclusion, rather than a beginning.
The office fight was interesting - most people who played HL would see a grunt using a mounted gun and think, "Ah yes, kill the grunt to stop it", and then feel confused when they can't shoot the grunt at all. I know I did. I don't know if that's bad or good, though: on one hand, confusing the player may lead to frustration, but on the other hand, it made me stop and think about what I really had to do, which gave this encounter a puzzle-like quality that I really enjoyed.

A couple nitpicks minor issues:

• The "battery" for the detonator is short enough to walk over, so it has to be pushed while crouching (or thrown with the Use key)
• If the player jumps on top of the armored vehicle near the detonator crate, he will fall inside it and may get stuck
• Some of the walls inside the office area look a bit too thin

All in all, there is some interesting gameplay going on, but the difficulty needs balance. Good luck!