First, I want to say that I do NOT know which bugs and missing pieces you know about and are working on, and which ones you don't. I know that this is an Alpha in development, so I am only going to make suggestions with this in mind, things I think need to be changed before other progress continues. Don't take it as insulting; I don't know what bugs you're aware of and not. This is the "(Chapters 1-7) WIP" version of the game, played Sept 9, '21.

I don't know USMC jargon, but if you don't either, get a marine to consult so the acting doesn't make military brats and veterans cringe.
It may be possible that some marines might refuse to kill an unarmed civilian if they believe that their orders to do so are illegal. Storyline needs to assure that they start out convinced that the scientists need to die before they start realizing that "I didn't sign on for this sh*t."
Ch. 2: I need you to put in captions for lines that haven't yet been recorded so I can get a sense of what I'm supposed to do. Whatever you have written, caption it if you haven't recorded it.
I don't know how many AI are supposed to follow me and when. Sometimes they do, sometimes I think they get lost. I don't know if there is a waypoint mechanism you're not using, or if it's just arduous work that takes a long time to perfect. I understand. I hope you add medics doing medic things, because I've frequently found myself needing their services.
Friendly fire is an issue that was inherited from BM. I think it needs to be turned off from the AI since it's probably hard to program the kind of fire discipline that trained marines ought to have. This goes doubly for them killing each other with grenades.

If target awareness is doable, make sure the tanks and other vehicles have it and that they know the blast radius of their guns before they blow up whole squads for the sake of killing that headcrab. A .50 BMG is more than enough.

Chap.3 was pretty short. I was hoping for more. The grate that has fallen into the elevator leading to the HSMS Facility is unbroken, and I get hurt falling on every time.

Ch.4
They really didn't call an airstrike on Freeman. Rather, it makes more sense to say he they "buried him alive with mortar fire, but we still haven't found a body."
The security guards with the .357s are insanely good shots, and some of them can take multiple headshots with the player's own.357 before going down.
By this point in the game, I noticed two severe flaws in design: the empty spaces, and the lack of hidden goodies. Valve's works are almost half easter-egg hunts for ammo and batteries. Everything in this game is easy to find.

Ch.5 The TOW missile launchers on the catwalks above the gargantua cannot achieve the angle of depression required to hit the target. Perhaps put something on the ceiling that can fall and blow up on the ground for the TOWs to hit.
The sound of the satellite rocket launch is coming from the wrong side of the map.
Trying to follow Freeman through the flooded industrial area, the vortigaunt ambush is too small and too underwhelming, making it really artificial. You need like 6 of them all surrounding and zapping me at the same time.
In the next cutscene... you call that CPR? A scientist might to that, but a corpsman would know to use his whole torso and keep his arms straight.
I also noticed that the turrets were a problem. I should be able to reposition them without them retargeting and betraying me and everyone else.

Ch. 6 the beginning scene does not have enough carnage and tragedy to warrant the kind of music being played. The atmosphere is not gritty enough, and it isn't really making a statement to the player. The whole map had way too much empty space.
The minefield has a lot of lost potential. Just a couple of headcrabs to whack or dodge isn't fun enough. We need more hapless aliens getting themselves comically blown to bits to make the long trek worth doing.
Encountering and passing black-ops placeholders (recommend you use security guard models instead of marines to avoid playtesters' confusion) camp required a lot of tries because of the lack of resources. Taking down the sniper by climbing a ladder without a grenade was annoying. Things got even worse entering the biodrome. I was furious when the lobby's ceiling turrets ignored the aliens in the room but only turned on when I entered.

Ch.7: Okay, I know what you're going for, but tanks should not be the slightest bit vulnerable to grunts and slaves. It's made of metal, and acidic beehives don't penetrate steel. The tanks need to be positioned in places where tanks can actually fit, and should be further back so as to be able to acquire a target.