Right, this review has spoilers and spoiling images
If requested, I can put the images as hyperlink instead of posting them straight on here
First off I'd like to say that I was impressed by this mod.
It was a pleasure to play and one of the few recent mods I've bothered to play.
That being said it wasn't without it's flaws.
Starting with the good points...
1) Visually gorgeous. The textures, lighting and sheer amount of detail in each room really sold the mood, the caves were beautiful and the lighting in the run down, abandoned rooms was pretty perfect.
You used volumetric fog and light flare to an effective degree
2) Good flow. Every room flowed naturally into the other one, meaning the mod as a whole can be played in one sitting without losing attention or getting frustrated
3) Reasonably challenging combat. I felt the large boss fight near the end was a tad difficult with the sheer amount of swarm facing the player. I had to kinda glitch this fight to pass it (see later on)
4) Good use of custom content. The Custom textures and most of the custom sounds were excellently used.
Speaking of which, that flashlight sound..
That is now my fetish
5) Some neat effects, such as the cafeteria and the black void door
However, it had many points I felt it could improve on. These didn't ruin the experience, but they are something to keep in mind for the future
Looking at Armageddon's feedback, I have to agree with him on some points.
The keys were a bad idea. I generally dislike keys in hl2 mods, and I'm sure some others will agree it isn't very effective as a puzzle.
Whilst the opening to the void platforming near the start was effectively done and impressionable, the actual jumping was a ballache and a half. I think either the platforms were too small (and too far apart) or I'm getting worse at fps games
Finally the pistol didn't sound right, agreed.
(However I loved the SMG sound, I know arma's gonna hate me for this)
Playing through, I have a few problems of my own.
1) AI. Whilst the combat was very well paced and the AI on the whole was acceptable for general play, it never felt really new or intense as other mods have shown combat can be.
The biggest case was waiting in this area and watching the combine rush down the middle straight at me where they could have taken side routes to make the combat more difficult

2) Glitches and Exploits. There were a few.
For instance the random shadowy dude you see running down the hall? I shot him a few times and he started following me. Rather jovially in a way

Also the last fight was too hard for me (I suck), so I just did this and camped it out on the sides

If you cant see I just stacked items to get back onto the walkways once the battle started
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Right, RANT STARTING
3) Pacing.
Not going to rant *too* hard about this one, but your pacing was a little off, meaning that any event that happened was a little underwhelming and anticlimactic
Especially with the horror aspect, it just wasn't scary. Actually it was until the moment you introduced the first zombie right at the start.
Horror is all about the ambience, the noises and the workup. In this case you started strong, working up and ratcheting up the tension only to blow it all on the old "zombie around the corner" trick.
From here, you never recovered as you either put in action (ceases tension) or you had too many cheap scares after each other without any workup.
For instance the scene where a body drops from a staircase and a shadowy figure blinks in and out was incredibly underwhelming (and almost comical). This is because you just had a "scary" thing happen just before and you hadn't ratcheted up any tension whatsoever.
The thing with horror is that the scariest thing isn't what's onscreen, it's what's in the players mind. Oftentimes good horror games will not have anything scary at all going on, but the ambience and prior events lead the player to think that something could happen at any moment.
And that moment when you've got the player thinking something scary could happen at anytime is right where you want them
For more examples, have a look at a new free game called "Slender", you can find it on youtube if you cba to download it, that has great examples of ratcheting up tension in this way.
Enough about that, the other issue was using combat in such close proximity to the horror elements without ever blurring the lines (like F.E.A.R did). It was somewhat jarring going from combat straight to scary again, especially with the lack of tension ratcheting. This meant that I was encountering the horror aspects while still in a combat mindset, underwhelming the experience tenfold
All in all your horror just wasn't scary past the opening, and I hate to admit it. There was one part later on which was scary (which I'll talk about later), but you didn't build up the suspense really and instead tried to throw odd imagery at the player which didn't really do it for me (like the shadowy figure and the bottle smashing)
Even the part with the fastzombie in the vents didn't have much of an impact because I still felt safe and not tense in my mind, which is something you need to work on in future works
TL;DR Horror isn't about the big scary payoff, it's about the lead-up to the payoff, making the player feel less and less comfortable until finally startling them with the grand scare.
The example game "Slender" I gave does an excellent job of this, I suggest you go and give it a try
RANT OVER
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5) The uhh...last scare
The last scare where you look up to see the poisonzombie was a truly excellent case of ratcheting the tension to then startle the player when they expect it (and then doing so from a direction they do not expect)
Unfortunately, I have to agree with arma, this was too much like Nightmare House 2 to really be excusable. You even used the same geometry and textures.
It's a great scare but it doesn't look good when you reuse people's ideas like that
OK, I'm done with the negatives
Overall it was an enjoyable play with a few minor issues that stopped it being truly memorable (mostly being issues with the horror)
A lot of the issues were my preferences and as such may not be entirely applicable
I congratulate you on a visually impeccable piece of work and look forward to a future more revised instalment
Uhh...I didn't make a list of things while I played through so I might have forgot stuff, feel free to ask me questions