Zynga's business model is like any other gaming publisher (such as EA, Blizzard, etc.). To succeed in gaming you MUST have a pipeline of games that continue revenue growth. If you cannot create your own, then you must acquire indie developers (OMGPOP recently). In time Zynga stock will be no different than any other gaming publisher stock. Look at Blizzard: other than Diablo, Starcraft and WoW, it has created nothing in the last 4 years beyond sequels. Homegrown innovation is nearly impossible.

Rovio was in the business for 5 years before Angry Birds, and I doubt they'll have another hit like Angry Birds ever again.

Id fell apart when it couldn't come up with something better than the Doom franchise.

OMGPOP was very smart to sell out to Zynga, because there is no way it would have come up with something even close to Draw Something in another 5 years.

Unlike rock stars and pop singers, creating a string of gaming hits is so much harder because it requires the perfect storm of so many variables each and every time, whereas a single person like Adele, Amy Winehouse, etc. can rely on their genius alone to create a hit.