The better half of Killzone: Shadow Fall is the multiplayer. If you want to give it a try, Sony has announced plans for a free multiplayer weekend. The game's online offerings will be free from December 28 through 31.
Of course, you don't want to waste precious time downloading the game, so you'll be able to pre-load the trial with tomorrow's PlayStation Store update. Once the trial goes live, you'll be able to play through any and all of the various Warzone features, with up to 24 players online. Then, you can spend New Year's Eve counting down to midnight... when your game will stop working.