Few words carry as much potential weight in the Geek World. The history of fictional characters from entirely disparate "worlds" is not entirely illustrious, but the lure of the concept is just too good to let a misstep here and there dull the effect. Who would win? Who's "better" in the first place? Will this special-talent be a match for that? Will the supporting casts show up? If so, what will they make of the meeting?
Can Captain Marvel ("Shazam" version) lift the Hammer of Thor? Could even Superman not break Wolverine's unbreakable adamantium bones? Is The Predator good enough to hunt The Alien? Krueger or Vorhees, who goes the distance? Very seldom are the actual PRODUCTS that spin out of the Crossover itself among the best of either "participant's" catalogue, but that's not really the point. The point is that "it" exists at all. That it happened. So-and-so and you-know-who occupied the same space, breathed the same air, exchanged words and usually fisticuffs.
If you were a video-gamer during the 1990s, during what is now remembered as "The 16-bit Wars," the possibility of ONE hypothetical crossover in particular loomed to some degree in your imagination. No use denying it: You thought about it. Pictured it. Discussed it. Today we learn that we won't have to fantasize for much longer. This year, as a just-announced mega-release tied-in to the 2008 Beijing Olympics (aka China's official "Planet Earth, meet the new boss" coming-out party) it finally happens...
Think about this: Up until the middle of yesterday, "Halo 3" was going to be "THE Gaming Event of 2007."