Critical Annihilation is a twin-stick shooter where every single thing is made out of tiny blocks, it also happens to be an incredibly satisfying experience.
Note: This game is currently in Early Access.
It came to Linux in Beta form back in October 2016, since then it has been promoted to official support with a nice SteamOS icon on the Steam store page. It's one that fell off the map for me, with so many titles (thousands since then) I forgot to ever check up on it. I decided to change that and personally purchased a copy. That was a very good decision too, because it's brilliant fun.
It has some of the most satisfying looking explosions I've seen for a while and—wow do the maps get messy! Take a look at this quick clip of me fumbling about in an early mission:
How awesome are those explosions? It's absolute madness.
There's many things to love about it, including co-op support so you bring a friend alone to blow crap up with you and it just recently in November added a model editor. It has a campaign to play through spread across many different locations, a survival mode and a very early start on a defence mode.
What's been the most fun has been switching between the different extra abilities you get. Want to call in a gunship? How about a flame turret? There's lots of awesome extras like that to really make it an explosive experience. Don't let the initial difficulty lull you into a false sense of security either, this isn't a game for kids as it does get a lot more difficult.
If you like twin-stick shooters, do try it. It's really pleasing that it's getting regular updates and the Linux version works really well, performance is great too.