Okay, more or less liveblog of thoughts playing the demo.
Going through the first CB, writing's decent, few complaints there. For some reason I had the impression this was set in the FS-verse, but it seems like a sort of parallel take on it? A lot of the terminology (Human Empire, so on) speaks to a different setting.
The first CB is well written but I have no idea who these factions are and no idea which one I'm part of. That could be a problem, hopefully I'll pick up on it in the briefing though.
Actually I do have one thing I really want to rag on. Did you have to lift a line wholesale from Halo Reach? That made me frown.
Briefing gridlines can be aligned (I believe by pressing ctrl-shift-L) if you are so inclined. They look a little ramshackle. There are some typos in the weapons as well but this is minor stuff.
I think my big issue coming out of the briefing is that I have no idea what's going on or who I'm fighting with. By this time in FS1/FS2 you knew what the war was about and what side you were on. However there's nothing else egregiously wrong with it; I know what I need to do.
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Pretty skybox, though it's a bit fuzzy and painted-on. I think you can probably get a better source to give it a sense of depth. The stars don't feel like points of luminance, they're more like droplets of paint.
I missed the first few messages because there were no beeps.

Wingmen behavior is a little weird. I can't give them orders, and the enemy has very long-range weapons. They don't break to attack until after the enemy gets in weapon range of the transports. Their tactics suck and this is frustrating. Wish I could give them some pointers with the command menu.
I lost a transport and command told me to depart even though there were still friendly transports under attack. Don't we want to help save them?

The Brackley jumped in and then immediately jumped back out, that was kinda janky.
I warped home, got a failure debrief, hit accept to replay, and got sent on the to the next mission.

There's a lot of potential here but I think you probably should've tested it a little longer.