I don't think I ever saw the original Madagascar, but that did not stop me from watching and enjoying Madagascar: Escape 2 Africa back in 2009. This one… eh, not so much. I believe the dialog is significantly less clever; there's no line comparable to King Julien's from the previous movie: "Bring me my nuts on a silver platter!" (It's OK: he was asking for a snack during a plane trip.)
The heroic zoo animals from the previous movie are itching to return to America. They'll need the help of the clever penguins, who are off gambling in Monte Carlo. Their adventures there draw the attention of Animal Control Officer Chantel DuBois (Frances McDormand, who can do a French accent just as well as a Minnesotan one). She aims to—literally—add the head of Alex the lion to her trophy wall. So the group finds themselves pursued, but they find shelter with a travelling circus (more funny animals with their own problems).
There is a lot of hyperkinetic slapstick and silliness, but maybe I just wasn't in the mood.