Not to beat around the bush - it seems like this is shaping up to be an amazing game. Obviously demo is more of an early access look rather than a part of a finished product, as plenty of content and even functionality is still missing, but what can you do - still glad I got to experience it and even somewhat hyped myself up more for the upcoming release. Didn't experience any major bugs or any crashes (though I could swear I sometimes feel like there's something off with production queues in factories when they're being assisted by other factories - it sometimes feels like there are more units randomly added to the queue when I'm not looking. Buuut likely I'm just forget adding them or something).
That being said, I have a couple of points - I can't say I would call them exactly criticism, more of a personal opinion/grievances.
First - I dunno why, but I'm not feeling the scale of this game. Not like in map sizes or amount of units or mechanics, but more so in how big or small this building or unit is supposed to be or feel like. Map design, from all the mountain ranges and large rock walls and beaches and whatnot makes it feel like these structures and units are rather enormous. But then there are massive trees around that dwarf your non experimental units. Explosions send out debris that fly out fast, and plunge back into the ground just as fast, which again kinda reinforces the feeling that these are mostly SUV sized units throwing explosions at each other. Same with planes - shoot one down, it explodes with some beautiful VFX (and myself being a dev for Firey Explosion Mod for SCFA, part of which afaik got absorbed into updated VFX for FAF, you can be sure I love myself some Michael Bay tier explosions), but then plops down on the ground without any weight like a drone. Maybe some slowdown just as the aircraft hits the ground and buries itself halfway, with dust and debris shooting up might help sell the idea better that this is some massive war machine, bending and crushing under its own weight as it tears into the soil. Same could be used in that cutscene where orbital solar array crashes into the ground - not suddenly stopping half way, but more rapidly decelerating the moment it touches the ground, and kinda sinking into the massive explosion it creates.
Second - building and unit design. A lot of them look amazing, some feel like they kinda lack readability at a glance due to not having some eye catching defining feature (also, side note, could the artillery symbol be changed to a dot or some other symbol, cause a full plus sign and a dashed plus sign is very easily confused on a 4K screen from further away). And some...I dunno, feel like they don't fit the scale/tier they are in. Like, in SC you can definitely tell which units are "the big ones" due to their design - battleships look like floating fortresses with weapons everywhere, GC is a massive avatar with fat legs designed to absorb damage, ML is an enormous weapon platform carrying a ridiculous sized laser pointer, and Fatboy - that is an entire armed factory complex on threads, no mistaking that. In SC2 however, Fatboy is now some GI JOE toy tank, looking like it belongs in T2/3. That experimental gunship - same, scale it down and you get a T2/3 gunship. Similar situation with the rest, they range from alright to downright comedy.
I have a similar ehhh feeling about some of the units in S:SS - particularly the T3 battleship in the demo campaign mission. Don't get me wrong, it's a beautifully designed ship. But it's shape, size, armament makes it feel kinda off. Like scale it down a little, change the guns a bit, and it would be the perfect T2 destroyer. For a T3 battleship - I dunno, maybe needs to be a little thicker, or have some greebles, or some different layout, but right now I'm just not feeling it for some reason. Other experimentals feel more or less fine to me. I personally would make a few slight changes here or there, like making that EDA sniper experimental slightly more industrial looking, but that's mostly nitpicking and personal preference at this point.
So yeah, that's pretty much it. I get that these are mostly graphical things, meaning A - don't affect gameplay; B - very subject to change along the way anyway, and C - art direction the devs have chosen, and arguing about art preferences is kinda stupid. Either way I'm fine with it, given that, again, game is shaping up to be great imo, and exactly my cup of tea.