(As I'd rather anticipated, I wasn't in the mood to do a Star Wars post, so instead here's a post about killing a different kind of imaginary aliens than the ones I'd have been talking about.)
Central Alien Agency is a game where you play as what's pretty blatantly a derivation of the Men in Black, with heavy influence from the movie/cartoon/comic franchise of the same name.
You're actually defending a crashed UFO or something, and when you're not actively fighting off the near-endless waves of alien monsters, you can take time to repair the ship; once it's fixed, you win.
As the above implies, you're a lone gunguy, and hordes of aliens coming in waves are trying to get you. You control the character with the WASD-arrow key substitution and the mouse (to aim and fire), and can buy new gear and other upgrades. (Ironically enough, none of the screenshots I took actually show projectiles being fired, though one does show an explosion.)
It's not exactly rocket science (other than the ship repairs, I suppose); it is, however, a lot of fun.
Below you can see four of the various types of aliens (of which there's a nicely animated bunch), including some kind of vaguely wolfish creatures, blue hovering entities, green airbag creatures, and big armored arthropod things.
And below you can see pretty much the same bunch and also a little bug that's the most basic enemy, blue bipeds with bazookas, and some rhinosaurish things.
And here we can see big hovering eyeball-worm-things that shoot eyebeams.
If you're wondering at the degree of influence from the MIB films beyond visuals, here's the most extreme instance, a gun that nearly exactly resembles the "Noisy Cricket" except for the recoil (and the fact that it appears to be as long as the user's forearm, which is probably a visual convention because the character model is so tiny).
It's also just as powerful as that massive explosion suggests. (Moreso, actually, because it's got a pretty decent firing rate.)
This is a pretty simple game that manages to capture an extremely fun formula and do that formula very, very well, that formula being "shooting game where you have a lot of targets." I could play this game for days on end.
Obviously, I recommend it.