Crimsonland is a top-down shooter in which you must defend yourself against a large horde of aliens. You use both the mouse and keyboard, moving with the keyboard and shooting with the mouse, similar to Abuse and Soldat.
After a large amount of kills, your character will gain a perk, such as faster reloading, extra speed, or some more outrageous ones.
There are four modes of play. Quest lets you play through several missions to unlock new weapons and perks in the Rush and Survival modes. Rush requires you to survive a fast, endless horde of aliens without any perks (it's hard to survive for more than 20 seconds). Survival is similar, except more forgiving: you play for points, not time, and you can pick up other weapons and gain perks against a slower horde. There is also the "Type-O Shooter" mode, in which you type out tricky words and odd combinations thereof to shoot slowly advancing aliens.
When the publisher Reflexive Entertainment ended their affiliate program, Crimsonland was one of the many games that was left without a verification source. 10tons has not found a new publisher, and it was not possible to purchase the full version of Crimsonland until it was re-relased on Steam in 2014.