I've tested it out myself and it's actually pretty damn good. Performance wasn't amazing, but the game is still in development and this is an early test build, but it's extremely promising that it works so well this early on.
Here's some shots from the Linux build on High details:
They've certainly managed to capture the feel of old-school shooters and it does look really quite lush. A bit odd having the retro style UI with such pretty environment graphics, but it works in a weird way.
Find the link to the Linux build on Steam here.
It's set to release in "Q1 2018", hopefully if the Linux testing goes well they might be able to provide Linux support at the release, that sure would be awesome.