Can a game that has “ridiculous” in the title be bad? No. It can not!
Even though I’m no fan of the multiplayer (zero-)gravity-shooter genre, I enjoy playing M.A.R.S., which features AI enemies and wingmen, various weapon types, upgrades and a pretty cool game mode, where a huge cannon will shoot at the planet of the enemy team of whoever is holding the remote to it. I also think it’s darn pretty.
M.A.R.S. uses shaders (but does not require them). The game menu is well-made in both look and feel too. The media license is not specified. Code is GPLed. M.A.R.S. runs on Lin/Win (get it here) and uses the SFML library (2.0, I had to get it from SVN).