Hi, I managed to play your demo, well done, it is quite polished.
I do have some feedback though, and as a previous user has pointed out, the environmental sound is sub-par.
The game experience you present would improve significantly with some decent voice acting. In addition, some chit-chat and backtalk between squad members (just a random selection of sound bites which play back when a squad member takes down an enemy or gets hit themselves) this will help alot with player immersion.
Secondly, the ship sounds and gunfire, they need more follow through or build up, maybe you should hear the weapons charging up or similar?
I'm no sound expert, but IMHO sound and voice acting are key elements to a professional feeling game (which yours is very close to being)
Hope that helps,