The audience would expect to see new things, meaning that much more of the story would have to take place outside of Andy's room. New characters would have to appear, including a new villain. And so forth. Toy Story 2 tries very hard to overcome these disadvantages and generally succeds. On a technical level, the movie is an overwhelming success.
Trees spread in green canopies, with every leaf digitally rendered.
A scene where Woody must navigate a minefield of cheese doodles shows every doodle in astonishing detail. The wizards at Pixar have done it again. As far as the characterization goes, Toy Story is fortunate to have a large ensemble cast of familiar voice talent that needs little introduction. Tom Hanks has the lead role of Woody the Cowboy, and it's hard enough imagining anyone doing a better job. Hanks has taken so many serious roles lately that having him play a role that reminds of the comic, childish side he sow famously showcased in Big is a real treat.