This is really neat, bonus points for providing a Linux version. I wasn't able to test out the multiplayer, but I can imagine it being fun with how the levels were designed. The basic gameplay is simple but really entertaining. More levels could be a great way to build further on this, if you want to update it. The setting makes for a nice Robin Hood-like story. The only criticism there I'd have is a really highbrow nitpick, in so far, as that it seemed a bit weird to me that I am going out collecting resources for a post-capitalist society... which were diamonds and precious metals, things explicitly valued not primarily for their use value but their exchange value and scarcity alone. Ironically, the radioactive barrels might have been the things most valuable as proper resources (OK, the mysterious crystals maybe too, and technically, there could be anything in the safe).
But that is a minor complaint, the game was really fun, hope it will get more eyes on it. Great job!