Developer Luxorix Games and publisher Alawar Premium are currently working on Space Robinson, an action RPG with a fun graphical style that's supposed to really test you.
Back in July, a user on Steam asked if they were planning Linux support to which the developer replied recently to mention they planned it. Now, they've actually gone ahead and put out a demo for Linux which you can download and try on Steam.
I've played it through myself and it's looking fantastic. Some really fun enemy designs that caught me a little off guard, with some that speed up and run towards you or sniper-like enemies that aim and dash. It even has support-types, with enemies that heal others which is quite unusual when these types of action games tend to put all the effort into just attacking. The weapons as well, they feel great and graphically it's quite nice too for a 2D shooter like this.
Reminds me a lot of Nuclear Throne, Enter the Gungeon and others like that but once again a small developer has come along to flip the genre around with some new tricks. I don't mean to be hyperbolic at all here but this could easily turn into a favourite. For a demo, it's really great.
While it has some of the usual suspects in terms of features like procedural generation for levels, roguelike gameplay where you die a million times, upgrades and more there is one thing a little different in this action RPG. It has a day and night cycle, which really does make it quite frantic as it not only reduces your vision it also introduces more and different enemies at night time. If you take too long, you might find yourself backed into a corner.
The only issue, is a typical GameMaker problem on Linux where gamepads don't seem to work currently. Do let the developer know in this linked forum topic what your thoughts are if you give the demo a go.
As for the full release, it's due out sometime later this year on Steam.