You are NUX, sole survivor of the Nexon warrior tribe. The evil Silthax has invaded your home world ..

Nux

You are NUX, sole survivor of the Nexon warrior tribe. The evil Silthax has invaded your home world of Nexolus, devoured your fellow Nexons and stolen the sacred power crystals from your village. Legend states that these crystals contain the power of life itself, and have protected your people for an eternity. They may even have the power to reverse the damage that the Silthax has done. With your home in ruins and only your ship and your trusty blaster to protect you, here begins your final mission. Hunt down this vile creature, rid the galaxy of its evil and recover the power crystals!

Minimum Requirements:

OS: Windows XP/Vista/7/8
Processor: Pentium® or AMD® 1.3 GHz
Memory: 128 MB RAM
Graphics: 32MB 3D Video Card

To activate the Steam key you've received, follow the instructions below;

First up, open the Steam client. (If you don't have it, simply click the "Install Steam" button here => Steam Store )
Sign in to your Steam account. (If you don't have one, click here to create a new one => Steam Account)
Click on the "ADD A GAME" button in the bottom corner of the client.
Then, select "Activate a product on Steam..."
Write down or copy-paste the activation key that you've received from GamesForPlay in the window.
Your game is now visible in your library! Click on your "Library".
And finally, click on the game and select "Install" to start your download.