As title reads, I absolutely love your game! I don't get why so many people give it shit still. I know that early on it suffered numerous issues with its performance, but outside of that and the early multiplayer (Which did get stale after awhile, though the Enhanced Edition has certainly remedied this issue, at least for awhile that is!) the game is amazing.
The maps have astonishing detail and complexity, every gun (though not necessarily balanced in some respects) feels awesome and unique. They all have noticeable impact (Though I will say, despite feeling sick, the stormbolter's lose much of their impact when you see just how ineffective they end up being t.t. Which really sucks cuz they are one of my favorite weapons in terms of aesthetics).
Now, more than ever, each class is useful and fills its own sort of niche (Though currently the Librarian feels rather underpowered, especially since you cannot select which abilities you use, unlike in the singleplayer). The voice lines, though understandably few, are very well done and especially with the new special missions can make for some epic moments and serious hype.
Even the Genestealer hordes, which by most games standards would be stale and boring (Considering their only real tactic is swarm, back up to regroup, swarm again) end up being challenging and fun to fight because of the excellent map design. They can sometimes just come outta nowhere, and I've gotten more than a few serious jumpscares when a stealther suddenly pops up and I spam parry in a panic, or when you hear not 1, not 2, not 3 but 8 of those annoying little suicide bombers all bumrushing your squad.
All in all, it's an amazing game.
But it's not without room for further improvement. I know I'm just one guy, and everyone has ideas and opinions about how to change things, but even still I feel the need to post up some ideas I had that, in my opinion, could drastically improve the gameplay (Though I understand that as a company you still need to consider whether it's still worth putting resources into this game T.t).
The first idea I'd like to put forth is one regarding the differences between the difficulty levels. Given that your game is relatively "small" in terms of scope (Though I have yet to get the same special mission twice, it is all on the same maps against the same enemies with the same weapons and classes over and over). I don't feel that a simple linear stat shift is a good way to go about increasing difficulty for the game. Take, for example, Killing Floor 2 (By Tripwire). They have 4 different difficulties, and through experience I can safely say that they are very well defined and certainly tiered properly. But, unlike many games, all of their enemies (Except, I believe, 2 or 3) do not scale linearly stat-wise as difficulty increases. Players do not lose health or armor, the vast majority of their enemies do not just gain HP or damage. Instead, the hordes that players in that game face get smarter and faster. Enemies start to run more often, they start using new tricks (One enemy even does backflips, on top of being naturally invisible, making it especially hard to hit) and moves. Instead of making everything a slog where you dump bullets into spongey enemies while avoiding taking hits to progressively thinner and thinner armor, the status quo of what is and isn't the case shifts. You have to take different actions in order to accomplish the same goal.
To get right down to it, I think a similar approach would certainly be appropriate for Deathwing, considering it bears a remarkable resemblance to Killing Floor in terms of the core gameplay loop. Instead of having enemies stats change, just have them behave differently based on the difficulty. The easiest difficulty they'd just swarm you, big lulls before massive, all-in attacks where the smaller enemies go in first, as the bigger and tougher enemies swarm over each other. This would be remarkably easy to deal with, as the difficulty suggests, beyond this, they wouldn't do much more. The next step up, the swarms get a little smarter. The lulls between assaults get shorter, they don't take as long to regroup. Smaller enemies will occasionally attack on their own or in small groups to keep the squad on its toes. This would resemble greatly how the game currently runs. Besides the more or less nuanced attacks of small waves with intermitten big waves, and a healthier mix of big and small bads that allows all of them to be more effective, they don't do much.
Hard mode is where stuff gets interesting. The horde becomes nearly relentless, lulls in the fighting are brief, what's more the enemies begin to cooperate in a more intelligent manner. The suicide bombers will start to use their allies as cover more often. Hybrids will run on spotting you, to avoid death, only to come back when the main assault arrives to peck and pester you (Or potentially land a killing blow in a fatal moment) while you deal with larger threats. The Brood lords and other larger enemies will be far less likely to attack by themselves, and all the enemies would rather coordinate ambushes (hiding around corners or behind obstacles) than just run down a long hallway. Furthermore, the enemy gains the ability to destroy the smaller, less reinforced doors (Albeit far more slowly than terminators can). Meaning that when you lock down that small door, its only a matter of time before the horde inevitably breaks through, giving a sense of urgency to every mission, even without a timer.
No Mercy is when things become ludicrous. The fighting never stops, hybrid psykers will use the hordes as cover for their attacks, while heavy stubbers and laser brutes will hang in the back wings to deliver their deadly payloads. Every turret is always online, and with the constant attacks dealing with them will be a challenge. There will be a fully fledged brood lord (Maybe even 2!) on every map, guaranteed on top of any normal spawns from your objective. And you can be sure they will open with surprise bioblasts or psyker storms before delivering their telltale roar and assaulting the front. All the while the smaller enemies will swarm the squad relentlessly, never retreating or regrouping, finding every flank possible while the players deal with the more looming threats. Furthermore, the suicide enemies now deal damage to the small doors, making them buy just that much less time for the squad to have their flanking reprieve. In No mercy, even the larger doors can't save you. As Brood Lords can break through them with ease, launching an ambush attack that opens with the sound of screeching metal as their claws pierce through the bulkhead, and slowly force the door open, making way for the smaller swarms to pour through.
All this, and the enemy's HP never changes. Acid splashes, bioblasts, none of them suddenly become OHK deathbeams. The swarms will be consistently killable, and the terminators consistently resilient. But even so, each difficulty would posses clear differences in their challenge level, appropriate for the difficulty. The players would even still have the option of turning on Friendly Fire, making an already challenging experience totally unforgiving.
Wew! That was alot to read! I'd do a tl;dr but there is no way of doing the suggestion justice with just a single sentence.
The rest of my suggestions are minor compared to that, mainly having to do with imbalances between classes and weapons.
The flamer is, hands-down, the best weapon. It has the same accuracy moving as it does standing still, it deals enough damage to wipe most things before they get too close (though when the hordes get especially thick even this monster has trouble), can hit multiple things simultaneously, and is also the fastest weapon in terms of melee response. The delay between letting go of the fire button and being able to swipe or parry is less than a half-second, which is easily 2 or 3 times faster than most of the other weapons (Which need to fully finish firing, and return to their resting position before you can parry). Making those few times where an enemy does get through easy to deal with with a quick parry and another burst of holy promethium. Its only drawback is it's pitiful range. It is incapable of dealing with turrets or other ranged enemies, and honestly that's the only thing keeping it in check in regards to the other weapons.
However, despite this, I think the solution is to only nerf it minorly (I'd just slightly reduce the DoT damage on the promethium burn, juuuuuust enough to make the bigger, more heavily armored enemies capable of pushing through it at least for long enough to force a parry or swipe), and buff all the other weapons that just don't compete. Namely, the Stormbolter (and mk. ii variant), the redemption bolter, and melee in general. The stormbolters, straight up, do not hit hard enough. For what they are, they just do not deal enough damage to be viable weapons. Combined with them having a laughable parry response (about a second between letting go of the firing button and being able to parry) their only real use is as an anti-hybrid weapon. They are just pinpoint accurate, but even when you are consistently headshotting genestealers they cannot even compare to the Spear of Caliban or Heavy Flamer or Hellfire bolter in terms of effectiveness. I think if the Stormbolter had a small AoE, that would fix it straight up. Just being able to hit 1 extra nid (Maybe 2 if the nids are particularly clumped up) on top of the main target would take it from being incomparable to being on even footing with the rest of the arsenal. It would make sense, as well, considering they are basically firing miniature RPG's.
The librarian just needs to be better. No real way around it, the force powers are too weak to be particularly useful on Hard difficulty, let alone no mercy. Let them choose what powers they take, perhaps as part of the customization screen where you equip effect reducers and stuff. Shit, even let them customize the powers like with weapons. Not much else to say here
And lastly, the melee. Oh man. I want melee to be good, I want so bad for it to be an effective playstyle. But the way the game is right now it just isn't. The animations are too clunky and slow, I get we're terminators but you're telling me I can't move my left arm to assume a parry stance while my autocannon's barrel is still spinning? Being able to quickly parry or initiate a swipe is crucial. I think that the non-melee classes should still need to complete their swings before being able to parry again, because they only have the one arm to parry with and it's busy swinging. But the Assault marines have no such issue. While one arm is swinging, the other should be able begin to assume it's parry almost right away. That would be part of why the assault marine is the melee god. It can just flat out parry quicker, which lets it be far more durable as a frontliner (especially the storm-shield variant). Melee damage is fine, the parry system is fine (if a bit clunky and hard to predict. Sometimes a slash that looks like it's going for my head hits my leg, or my arm or something. But that feels more like a bug than an intended aspect of the design). It just needs to be a fair bit easier to actually use these systems. As it stands it's nigh impossible to deal with the nids once they are up close, even as an assault marine.
Anyways, I hope this gets to someone up there! Thank you for taking the time out of your day to read this, and especially thanks to the entire team for giving us this awesome game! I hope it gets some more love soon!