If you don't want to read about the ending of Killzone 2, then move along, otherwise read on.
After a tough final boss battle against Colonel Radec of the Helghast Army, you meet up with Emperor Scolar Visari in his Helghan palace, who you've been searching for throughout the game, You're supposed to arrest him and bring him to justice, but his army has killed many of your men along the way and you're not the forgiving type. He warns you that if you are to kill him, his armies will rise and will fight to the death in his name.
Foolishly, you ignore his threats as you think you've killed off most of the Helghast in the game, and the rest will back down with no commander behind them. You kill him and think that the game ends there, but when you walk outside of the palace you're greeted with the sight of dozens of Helghast drop-ships filling the sky. "The Madness Begins," are Visari's final words.
Stay tuned for the Killzone 2 review.