Before Valve crossovers were mere fodder for pre-purchase exclusives and newly released PC ports on Steam, Peggle Extreme dared to dream, by offering Orange Box customers a unique journey into a world where Peggle, Half-Life and Team Fortress collide for no apparent reason, creating a unique story where cute animals from Peggle rebel against the extra-dimensional invaders of the Valve multiverse (here portrayed as far more genocidal than Valve would have liked). In fact, it's the same MacGyver-esque plot device that Valve resorted to when they created the Perpetual Testing Initiative story for Portal 2. Mere coincidence????
... Okay, setting aside the fanman sarcasm, Peggle Extreme is really fun, mildly replayable, and worth trying if you're ever... bored, I suppose. Give it a try!