This OP is from like 2010 holy stuff it's still useful:

What is it?
It's a physics-based 2D side-scrolling shooter with pixel-y graphics, crabs, mod ability, lots of gamemodes, a pretty neat AI, rather varied mod support, the ability to cram a stuffload of crabs into a crate as an ad-hoc bomb, and (as of build 30) Steam Workshop. Seriously this game's pretty neat overall, check out out.
Screenshots
(one of these images is out of order, will replace later)
Story
Earth was over.
Once peaceful, our world was awash in bloodshed, wracked by wars backed by holy men. It was humanity's darkest hour, and the boldest decisions were simply all we had left.
Forged in the rush of war, a curious symbiosis between man and machine formed. Our numbers bleeding away, technology enabled the survivors to control robots and clones from safety. And in the end, we found our bodies an obsolete constraint, and cast them off. Brain and mind interfaced with machines, we became more spirit than flesh-- one person living through many bodies.
And in this new form we attained escape from the corpse of our world. Interstellar rocket ships for the decades-long flights to reach new worlds became common once life support for entire bodies was unnecessary.
Fleeing into the dark unknown, humanity discovered it was not alone, but also not important. Humanity struggled for acceptance in this alien community, eventually forging the Orion Spur Amalgam. Interstellar trade flourished, and with it came rapid expansion. As the era of faster-than-light dawned, humanity could live again in peace and prosperity.
But human nature wasn't cast off as easily. For every city and space station compounded the ever-growing hunger for resources. Worlds were stripped in civilized sectors where law ensured conquest by the highest bidder. So all eyes turned outward, to star systems where no law existed but what you could enforce.
As the gold rush brings commanders from several rival groups to one such world beyond the far eastern fringes of the OSA, all prepare to assume... Cortex Command.
Links
Downloads

MORE INFO ON THE COOL ASS NEW UPDATE GUYS LOOK-- --
YOU CAN NOW CONTROL MULTIPLE GUYS IN A GROUP.
SERIOUSLY CHECK THAT stuff OUT

HELLA
Ther are also achievents, Steam Workshop and miscellaneous fixes. Those include but are not limited to SMARTER BRAINS AND SNIPERS, computer-controlled goons getting smarter and better overall, etc. A change-log can be found through the link above.