The original has multiple instances of hundreds of penguins dancing at once in rhythm. Sure, it's CGI so it's pretty easy to make for a halfway skilled animator, but it still looks and sounds awesome.
And then there's Mumble, the Adelies, and Ramon braving a windstorm.
And the scene where all the male penguins are tending to their eggs and braving the snowstorm. Also Truth in Television.
Back-flipping Emperor Penguins. Enough said.
The sequel has the spectacular climax where Penguins, Elephants Seals, Krill and one puffin, together give themselves one more chance to save the Emperor Penguins by pounding and dancing on the ice mass to a magnificent rendition of Queen's "Under Pressure."
Prior to that, Erik delivering an epic verbal smack-down to Bryan a la opera.
Erik suffers from what appears to be textbook social anxiety; unlike his father, he's perfectly capable of both singing and dancing, but is too terrified and insecure to relax and let himself be that vulnerable while surrounded by other people. It's severe enough that he "whizzes" in public when he makes a mistake that most of his friends would laugh off, and sometimes has panic attacks because he's experiencing intense emotions and has no way to release them safely, as seen before the Bridge of Light sequence. All this combines to mean that a single line—delivered in a deep, pure, unwavering voice—is enough to give the audience chills.
"...And the kings are all fools..."
And between these two instances is about twenty seconds of a spectacular rendition of "Rawhide" involving the elephant seals.
Originally, Mumble would have lost his fluffy down when he was falling down the ice cliff to chase after the fishing boats. It was such a last-minute decision to keep him fluffy in the final cut that, thankfully, the storybooks for the first film still keep the original storyline. ◊ ◊ ◊ ◊