I finished Half-Life: Alyx on 2020 November 19. Disclaimer: I never played the original Half-Life. This was my first exposure to the franchise, so I won't be commenting on the story much.
Overall opinion: middle of the road. A weak but inoffensive story, full of bad excuses for puzzles, some serious formatting issues, but good combat.
I played on Hard. The balance was a bit on the easy side, but enjoyable.
It uses the freeform save system, meaning you can save inside of a fight. You can save after every kill if you want, and load a save if you ever take too much damage or waste too much ammo between kills.
This sucks because I have a completely gradual tool that can easily be used to trivialize every encounter. I don't like save scumming, but I do it to some extent in games that use this system because it means they balanced it with the assumption that you have this ability. Especially because boundaries between sections are not clear in this game (there are a lot of places where I would've put a checkpoint, but you're still fighting in the same room), not to mention all sorts of status is preserved even across chapters so it doesn't even really have sections, you can't be expected to "do the honorable thing" and only save inbetween sections.
Health is arguably not even the main form of status. Running out of ammo was a constant near-issue for me for the entire first half of the game, to the point where I was happier to find ammo than to find health; and that's from a playthrough where I loaded a save when I missed too much. You don't have a melee or any other backup form of attack - if you run entirely out of ammo, and there isn't some laying around for you to pick up, you have no choice but to load a save.
Related to that: exploration is an important and boring part of the game. Important because it's the main way you find ammo, boring because "exploration" tends to mean opening every drawer and box you come across. They're everywhere and most of them have nothing, but you have to check them all to find the ammo you need.
Aside: there are random objects all over the game world, like soda cans and cigarrete containers, that you can pick up but have no purpose. All they do is waste your time, because they often look like ammo at first so you have to check.
Other aside: the level designers have a weird fixation on bathrooms. When you're fighting through houses, it seems like every other room is a bathroom. Sometimes there's ammo in bathtubs.
The combat is pretty solid. It's a shooter with non-regenerating health, which I like - health is a mistake buffer, not something you drain by trading shots intentionally because you know it'll regenerate. It avoids the pick-off slog of Halo because enemies come after you, and more importantly, Combine soldiers can deploy Manhacks (flying drones with spinny blades that chase you) so taking your time will cost you more ammo and health.
Gunfights with Combine soldiers feel pretty good in VR. You have to think a lot about sight lines because they move around the battlefield, and if there are mutiples, they'll often position themselves so it's hard to be covered from all of them. If you duck behind cover to avoid fire, you can't peek back out the same side until they're reloading. A go-to tactic of mine is to peek out the other side, alternating for each shot.
I wish headshots made more of a difference. I don't know how much it is, but it still seems to take at least 6 pistol headshots to kill a Combine soldier. It never feels like headshots are worth aiming for, which removes some depth from the combat.
The "puzzles" are the worst aspect of gameplay. I don't think there's a single good one. There are 2 categories of bad puzzles here:
Puzzles that are just a matter of "inspect the environment until you notice this, and as soon as you do you've solved it".
Most of these are at least reasonably solvable, but there are several Guide Dang Its which I shamelessly looked up (and never felt stupid after seeing the solution). I think the worst example is this door. This is near the end of the game and is the only electricity flow puzzle where timing is a thing. The entire rest of the game trained me to think that in electricity flow puzzles, turning power on or off updates the entire grid at the same time.
Puzzles that are pure busywork. You do puzzles to open some supply containers and to activate upgrade stations. They don't take any thinking to solve, they're just pointless exercises that either don't have a failure condition at all or there are no consequences for failure. So why make us solve the puzzle? It seems like they took inspiration from the Mass Effect 2 hacking puzzles (which were a stupid pointless part of the game but at least they were quick, easy, and optional).
And lest you think I just don't like puzzle games: Portal is one of my favorite games. That's because Portal puzzles were puzzles, not just exercises flavored as puzzles. You were told the rules and it was up to you to figure out how to use them to reach an objective. Every Half-Life: Alyx puzzle is either "follow these instructions and try again if you mess up" or "we're not telling you what your objective is, but you win as soon as you figure it out".
Honestly if I had to guess, the only reason the puzzles are in this game is so people don't see it as a shooter. It is a shooter, but it doesn't feel like one, and the puzzles are part of why.
There are still some story critiques I think I'm qualified to make, even though I haven't seen the other Half-Life games. I did look up a plot summary of Half-Life 1 and read some of the Half-Life wiki to make sure there wasn't context that resolves my criticism of the G-Man, so I'm not complaining because I jumped into the middle of a story.
The scene where Eli is saved is a Deus Ex Machina because not only was there no expectation that the Vortigaunt was on the way, not only it is an unacceptable coincidence that he just happens to arrive at that moment, but he also told Alyx he wouldn't be coming. Actually he told Alyx that Eli was already dead and that was never mentioned again.
The whole dream house sequence at the end was disinteresting and just reminded me of the dream sequence in Fable 2: random unexplained surreal stuff because we want to make it epic. The encounter with the G-Man at the end is cringe that sounds like what I wrote when I was 10. He's an unexplained seemingly omnipotent space god who feels like an author insert: he tells you how impressive your work was, how special you are and how you're the first suitable replacement for his previous subject, Gordon Freeman, despite Alyx being basically an ordinary human, which contributes to the feeling that G-Man is not talking to Alyx but the player; he is the writers breaking the fourth wall and his dialogue makes him seem infatuated with the game. Even his voice sounds cliched and irritating and he talks too slowly, and him standing in your face in VR didn't make the scene any better.
The periodic chatter between Alyx and Russel throughout the game is much nicer than just having hours of exploration without dialogue or plot development. Their writing is decent, and it helps humanize them... in a minimal sense. Alyx is still totally nondescript and personalityness. That reminds me: Alyx expresses fear in dark places early in the game, but not when heading into a battle with half a dozen Combine soldiers. That's backward. It's really rare to see a work of fiction in any medium where fear of battle is meaningfully portrayed.