Investors are a skeptical lot. They showed that today after Zynga debuted a bunch of new games and services for the next generation of social games.

Zynga’s stock fell 5 percent Tuesday to close at $5.76 a share during normal trading hours, giving the company a market valuation of $4.25 billion. That’s well below the $10 a share and $9 billion valuation from the company’s initial public offering in December.

During the event, Zynga unveiled new games such as The Ville, ChefVille, Zynga Elite Slots, Ruby Blast for mobile, and Matching with Friends on iOS. It also described new features such as synchronous multiplayer play for its Zynga with Friends Network. And it offered a glimpse of FarmVille 2. Some observers dismissed these titles as derivative and unoriginal.

Beyond its own games, Zynga described offerings it’s publishing for other developers. It unveiled the Zynga applications programming interface (API) for speedy and more efficient third-party games, and it talked about four new third-party developers on its Zynga Partners platform, including 50 Cubes, Majesco, and Portalarium.

Zynga also announced its new Zynga Mobile third-party publishing program with partners such as Atari, Crash Lab, Fat Pebble, and Phosphor Games Studio. Sava Transmedia showed off its third-party game, Rubber Tacos, which will debut on and Facebook.

Colin Sebastian, an analyst at Baird Equity Research, said that investors were probably expecting more than “more of the same.”

Michael Pachter, analyst for Wedbush Securities, said, “I think people expected a lot of completely new experiences, though I did not, and were disappointed that the new games were similar to old ones. I am not really sure what people expected them to do differently.”