When asked about a Linux version on Steam, the developer replied with this:
I'm looking into it!
If it seems like your sort of thing, if you want to show your support you can do so in this forum post.
About the game:
Let Them Come is a fast paced pixel art shoot ‘em up. Twitchy trigger fingers and focused battle tactics are the order of the day as wave after wave of alien-like creatures try to take you down. Gameplay is simple to pick up but hard to master - only the best of the best will survive to fight another day. With a variety of alien creatures to mow down and cool weapons to do it with, stylish retro backdrops and a hard rockin’ soundtrack, Let Them Come is a fast and furious pixel style shooter on steroids.
The idea behind the game seems pretty simple, with your character being unable to move, but it does look really quite fun. The style of it is great, with the sweet pixel art style, with a little gore thrown in looks like my kind of game.
Something about it reminds me of the scene from Aliens where the automatic turret is just firing away in the corridor, love it.
Thanks to HexDSL for telling me about it.