Thanks for making a Linux version of the game, I played through all that is available in demo, here are my thoughts.
The black text on dark background in the merc control UI buttons lacks constrast, the transparent backgrounds can cause readability problems too depending on what's behind them. "Range" text can sometimes blend in with the background, an outline would help. The tutorial speech bubbles that point to in-world element stay fixed and move with the camera. I would like to be able to see the AP number on tiles from behind walls, so I don't have to turn the camera just to see that. On that note, I think it'd be better if instead the remaining APs were shown on the tile instead of AP cost, so some of the math is already done (Xenonauts is a game that does it this way). A cover indicator, using a similar system to the UI element that shows much of a target is visible would help to remove some ambiguity from some cover elements.
It's cool how the hearing gets reduced when you take a shot.
The beginning 1v1s were not very interesting at all, there's not many tactical options available then, and it puts too much importance on an individual unit, allowing cases with no recourse such as what happened to me where I got hit by a grenade, lost all APs, then got stun locked by pistol shots for the next 5 turns before dying. In fact I think the number of units you can have in this game is very low, having just 2 is fine for the very first tutorial battle, but by the end I only had 3 units, I believe 4 should be the minimum, with the possibility to get more.
It feels very strange to never need to reload nor have to worry about spare ammo in this kind of game, resource management is usually a key element to this style of game.
The AI can make some questionable grenade throws, had a case where it tried to throw a nade at one of my units, but it bounced off a nearby wall and killed another enemy instead.
I hate having to drag from a merc to a tile to move, you should just be able to select a merc and then click a tile. I wish I could control the camera with WASD, changeable keybinds in general is always good to have too. I noticed right click also does nothing currently, maybe make that turn the merc instead by default, or make it change fire mode. I don't see why there needs to separate keys and UI buttons for standing and crouching, just make it a toggle.
Diagonal movement costs the same, that's ~41% more distance covered per tile for no extra AP cost, other tactical turn based games often make it cost 50% more AP, which is a close enough adjustment.
Footsteps sound quite loud and weird.
The different death animations are quite good, I liked how specific they get, like with the one where they hit their back against a wall and then fall over.
It's kinda weird how when the roof disappears from a building when you get close the lighting acts like it's physically gone, only casting shadows from the walls, perhaps keep the roof shadows but add some interior lights.
It's also weird how it seems you don't need visibility of windows and such to get roofs to disappear.
I had a case where a building way across the map had its roof removed.
And another where I got close to one building and it also removed the roof of one that was farther away.
I like how there's many factions that are not friendly with each other, and how you can take advantage of that while they're distracted with each other in some big fights.
I noticed there's a lack of usable doors.
I had weapons sometimes increase accuracy after taking a shot, I find that strange.
There really should be vaulting through windows, and similar low objects.
It's sometimes difficult to tell what is visible to a merc and what isn't, maybe have the tiles that aren't visible be darkened, the game already has some visibility UI element with the interrupts.
I feel this game could benefit from a suppression mechanic, for more tactical options with burst and auto fire. This could give a reason to have a free aim option too, perhaps that's another thing right click could be set to do.
I noticed attacks don't trigger interrupts, but maybe they should. I also had an enemy walk diagonally in between two of the interrupt trigger tiles, which means there's basically dead zones when you're watching an area at an angle with only the first level of interrupt skill. There was one case where I moved one unit northeast, and it triggered an interrupt, but the enemy targeted an unit further south I had already moved previously instead.
It's interesting how there's both a purchase system and a "learn as you do" system for gaining skill points.
Consider making it so you can safely shoot over your own units if they're adjacent and crouched, feels a bit jank to have to move around them in those situations (that's another thing Xenonauts does), maybe you could make so if you shoot over an unit this way they also have their hearing reduced as if they've taken a shot.
The "close to wall" animation seems to override the "in interrupt mode" animation.
I noticed there's different "classes", like "scout" and "rifleman", what's the difference? I don't think the game explained it.
I had one case where I dropped a nade so another one of my units could pick it up the next turn, but then a Ben Dabi unit that was previously idling in a corner with little HP, walked up to it, stole it, and proceed to idle in the middle of a doorway blocking my path as well for the next couple turns, it decided to move and do some shooting after.
I'm a fan of shotguns but this game has none, hope some will be added in the future.
The enemy AI is... Not very good, even on very hard, they have a tendency to bunch up in the middle of roads and shoot without seeking cover, rush where I have units waiting for them, sometimes walk back and forth and do nothing else as if they're indecisive, or, when retreating, all run simultaneously to the same wall in the map, and line up side by side in an easily flankable position.
Sometimes some weird shadows appear on the top left of the screen depending on the camera position.
There should be a way to plot a path through the overworld.
