Cobalt—Mojang's Not-Minecraft platformy, shootery robot game—is currently free on Steam. However, it's only free on Steam for this weekend, so be sure to git downloadin' if you want to shoot other robots in slow motion.
There doesn't seem to be a Cobalt review on PC Gamer, but the Steam reviews are "very positive", and there's a 33% sale on at the moment if you'd like to keep the game forever after the free period. That free period ends at 9pm GMT on Sunday night, 1PM PST Sunday afternoon, or whenever that is in your local timezone.
These video introductions to Cobalt's various systems might be worth a watch.