You need to get your ass to Mars and buy a copy of Jamestown on Steam. It’s down to $4.99 today, which is half off the normal going rate. For that money, you’re getting a remarkably well-made indie shmup about 17th-century British Colonial Mars. You can’t ask for much more, honestly.
In addition to Jamestown being one of my personal highlights for this year, it features my favorite game soundtrack of 2011. It’s particularly worth grabbing if you can get a friend (or three) to play through the story and bonus missions in co-op mode. Either way, I cannot recommend this one enough.