Make Sail from developer Popcannibal is a reasonably promising game about building boats and attempting not to sink. The latest update is out and adds in a creative mode.
One I spotted recently, Behold Studios (Galaxy of Pen & Paper, Knights of Pen and Paper) are working on a new game called Out of Space and it sounds interesting enough.
For those of you with a creative side that fancy building a theme park, Parkitect is a good option. It's currently in Early Access and progress is great.
After waiting since last summer, Behold Studios have now managed to add official Linux support to Galaxy of Pen & Paper along with the +1 edition free update.
Epicinium from developer A Bunch of Hacks has hit Kickstarter. It's an interesting strategy game, one where nature is a finite resource you must try to not destroy during your war.
Klei have been working on improving Mark of the Ninja: Remastered with a recent beta that's now live for everyone. Two Linux-specific issues were found and fixed.
Jellies, yes Jellies. Little wobbly creatures not too different to the slimes from Slime Rancher. Alchemic Cutie isn't just a cute name, it's a sweet looking game.
Planetary Annihilation: TITANS, the massive scale RTS now being continued by the new Planetary Annihilation Inc had another small patch recently to further improve it.
Since Steam has relaxed their content policy lately, Meltys Quest has not only become fully uncensored it also now has a Linux version so you can go about and do the naughty.