The Po (Jack Black) of the first Kung Fu Panda is still the same goofy panda with a strong spirit and unique karate moves, but in this movie he faces unanswered questions about his past. While the first movie was more of an origin story, the sequel shows his quest to find out where he came from, a gap that he needs to fill in order to become at peace with himself. If you wondered how a panda could be the son of a goose, your questions will be answered, and Po's backstory is much more emotionally developed than you might think.
Po also has to confront the villainous Lord Shen (Gary Oldman), an albino peacock. Tai Lung (Ian McShane) in the first movie relied more on brute force, but Shen is much crazier and unpredictable. In typical supervillain fashion, he plans to take over China and destroy Kung Fu forever (yes, Kung Fu is treated pretty lightly in these movies, but there's enough philosophy involved, and it is a kid's movie). Though Tai Lung held a personal grudge against Master Shifu (Dustin Hoffman) in the first movie, Shen is a more fitting antagonist for Po because of a strong connection to Po's past.
And of course the colorful supporting cast is back too. The Furious Five are all well-designed characters, and although they don't have much speaking time, they all have their moments to shine (especially Angelina Jolie as Tigress and Seth Rogen as Mantis). Though Jackie Chan barely had any lines. The new characters all help to expand the world of the movie.