I just want to start by saying the game is fantastic. I have already given it good reviews elsewhere on steam and other places. I would give it a 9 of 10. Here I am going to post the reason it is not a 10 of 10 game, and I feel it could easily be.
Two major issues and missed opportunity.
-Sound effects- I just realized something walking into a room of head crabs scurrying around. There was a major missed opportunity with this game. It was pretty scary walking through that door and seeing those headcrabs jump out. But I realized something was missing. It would be so much more terrifying if I could NOT see them, but I could HEAR the soft shuffling of the headcrabs around me when there close. It would need to be subtle and very faint, but it would be scary and panic inducing.
In fact that is my biggest complaint about the game. The alien calls and soldiers shouts are all fantastic, but the sound of enemy movement in this game is basically non existent. There is no background music, so like Dark Souls, take advantage of that fact!
-hard difficulty- Hard mode is not hard at all in this game. And it is not because the ai is bad at all. It is very good in fact. It is because you have a ridiculously high amount of health with a full health and a full shield. Enemies die realistically but you do not. That design philosophy is fine, Gordan freeman is a badass and that should be so. But it needs to be balanced around that fact. They can literally double the amount of enemies and it would still be playable. Now I am not saying to do that for every encounter, I think the military fights are actually mostly fine, though a few more Marines in a squad in hard mode would be nice, headcrabs, zombies, basically all alien encounters are a mediocre challenge at best. Now of course we don’t want to turn this into a different type of game so I am not saying put enemies everywhere. In fact, keep them where they are. Just adjust those encounters and tweak them a bit to increase the challenge.
-More teleporting in of enemies during the encounters when they already teleport in. Have a second or third or fourth wave come in much more often for the Zorg and Agrunts and headcrabs. I can end most encounters with the at 75 % health or better. Keep em coming. Also, have some enemies teleport in behind you. It makes no sense that they just teleport in directly in front of the player in his line of sight.
-Zombies. Zombies are no threat at all and only require a crowbar. The entire facility was just taken over by aliens. People would group up in clusters. I shouldn’t be fighting one lone zombie over and over after maybe the initial reveal. They should be in groups of four or more and they should be accompanied by head crabs because that is how they turned. Perhaps add a non shuffling zombie variant that moves a bit more quickly. For example, it makes sense that the scientists are slow, they are out of shape and the zombie should reflect that. However the security zombie, and especially the marine should be faster to reflect the physical shape of the body that was taken over.
-head crabs. They are also no threat. They can jump across the screen so fast but they move around as slow as a turtle? Give them actual walking and turning speed please. They are the size of a small dog or cat with long legs so they should be able to move faster.
-Those alien spit enemies ai could use a tweak as well. I can attack them from far a way and they seem to not respond at all. They have a long range attack have them chase after and move more to get into firing range during a long range battle. Make the behavior more aggressive and give them a buff to movement speed as well, leave there turning speed slow but give them a fast bull charge ability.
-The AI for the marines is very good. They flank you, the move around very quickly and the advance on you like real marines would. They need no change.
Most of the other enemies are pretty good for the most part balance wise, just like I said have them cluster in larger groups together. It makes sense from a lore perspective as well. The game is fantastic though even if I feel it is very easy.