Just want to say this map is fantastic, especially when the combine start to appear that's where it gets seriously fun. The map glitched out at one point and I had no bother going back and restarting one of the fight scenes because of how much I was enjoying it, it's a good blast.

I want to give some suggestions and such so you can better improve this map, and just report on how you can make this map just that much better.

1. The Keycard Problem
When I got to the safe and opened it, I knew exactly what the keycard inside of it was for, only problem was mid-fight against the combine I somehow lost it (probably from scurrying to put an item in my wrist inventory slot mid-fight) and when I made it to the elevator I somehow lost it. Took me ages to try and find, eventually I had to restart the whole fight scene (I honestly did not mind, was so much fun).

Instead of using a keycard to unlock the door in this instance, I think it would be better if you just activated something that unlocked the elevator door. Amidst the chaos, I found it easy to lose the keycard and having to spend a lot of time tracing my pathing just to find the keycard to continue.

I feel it's less convenient to have one less slot just for a keycard.

2. Atmosphere
I really like the detail you put in this map, but I couldn't help but feel something very important was missing from it: sound.

The environment you made was compelling, but I just couldn't sell myself on it without any sound whatsoever. I'm not sure how it works in Source 2, but in Source 1 you would have soundscapes in rooms that changes what type of sound environment the player listens to. You could add other simple looping sound cues like ventilation noises, electricity sparks actually making a sparking noises, etc. After playing the official campaign and going into custom maps, I realised how important sound is to really sell the environment you're making. It's extremely immersive and keeps the player engaged.

Another thing is I feel the starting ambient music that plays as the map begins loops way too frequently and got quite annoying.

3. Everything else
There were quite a few bugs when playing. The first bug I encountered was all of the keyboards in the map I could see through the walls, they all looked like a red wireframe. I'm not sure if that's something local to me I just thought I'd give it a mention incase it's not.

One of the blue headcrabs' AI got stuck. In my first play through, one of them jumped in a body and didn't know what to do with itself afterwards.

At the very end of the level, I got permanently suck and had to revert my save to almost the beginning. Whilst trying to throw grenades into the cages higher up, I wasted too many and didn't realise I had a limited supply, I even started using them on the combine. I think having another batch of grenades that you have to do a hacking puzzle would be nice. Even if it's just 3 more.

I noticed something off with the buttons on the elevators, and the xen prop placement. From what I remember I think the buttons were placed not totally on the wall (floating away from it), and the Xen stuff was floating off the floor a bit where the barnicles are with the hacking puzzle.

4. Other suggestions
When doing the hacking puzzles, I suggest putting objects in the way that you have to move out of the way in order to continue following the trail. It's always fun having to throw objects out of the way when trying to do one of those circuit puzzles.

Conclusion
The map was fantastic. It's the most fun map I've played on the workshop so far. The suggestions above would make it a million times better and really sell what you've made to the player even further.

The combing fights by far were my favorite, there was just so much action all at once, something I felt was missing from the official campaign. The music makes you feel epic as you lob their grenades back at them, whilst doing a 180 to blast the other combine soldier's face from above. You definitely utilized the map well, making the player back-track through the same parts of the level only to be met with even more combine.

The ending was fantastic, the man hacks annoyed me a bit, but I realised that it made that part of the campaign much much more intense. The limited space to fight the masses of the combine made me roll around on my floor unintentionally, little to no ammo, scared ♥♥♥♥♥♥♥♥. It was a blast.

You did things in this map that I feel were missing from the campaign. Mainly the huge, huge combine fights, especially the one where you have to do a massive standoff against them. Extremely fun.