The last time there was a leak of this magnitude was in 2003, when a large amount of Half-Life 2 was released onto the Internet. In that case, the game was only partially finished and Valve were able to rework the game's code and structure so that it was not compromised too badly by the leak.
In this case, the leak is far worse. Crysis 2 is much closer to release and the leaked version appears to be mostly complete, consisting of the full single-player game, access keys for multiplayer and the CryEngine 3 game editor. CryTek have not responded so far, but publisher Electronic Arts are understandably furious, releasing the following statement:
"Crytek has been alerted that an early incomplete, unfinished build of Crysis 2 has appeared on Torrent sites. Crytek and EA are deeply disappointed by the news. We encourage fans to support the game and the development team by waiting and purchasing the final, polished game on March 22. Crysis 2 is still in development and promises to be the ultimate action blockbuster as the series' signature Nanosuit lets you be the weapon as you defend NYC from an alien invasion. Piracy continues to damage the PC packaged goods market and the PC development community."
The game has been in development for about four years and has cost tens of millions of dollars to develop, so the leak is a serious concern for both developers and the publisher. However, finding a silver lining, players of the leaked version seem to be near-unanimously proclaiming it to be an excellent shooter, ramping up the anticipation levels which previously had only been fairly modest.