I watched this today with two of my younger sisters, one of whom regarded the first movie as her "favorite movie ever" (before Kung Fu Panda came out) and was really excited for this sequel. As soon as the credits rolled, she commented "That was... off."
(Spoilers! Spoilers! Spoilers!) First of all I'd say that the visuals were amazing as before, as well as the music and choreography. But the plot... it reminded me of how I used to put my iPod on shuffle and make up stories to go with it. A whole musical number just to calm upset Erik down? A bunch of elephant seals singing while stampeding? I was generally surprised and not sure I should be humored or facepalming at the inclusion of "Never Gonna Give You Up" and "Dragostei Din Tei." I mean did I really have to get rickrolled by krill?
Oh and the krill. I kinda sorta liked the idea, but their almost pointless side-story had me rolling my eyes. The audience we were with seemed to like them, though, and laughed every time they appeared. So I guess YMMV.
There were WAY too many accents and half the script was lost on me as I tried to process what each person was saying, having to quickly switch from American to Spanish to Swedish (Romanian?) to Indian, etc.
The environmental message was even more heavy-handed this time (tufted puffins apparently all killed off, oils spills, global warming, etc.) I agree we should be concerned with these, but the constant shoving of it in your face makes you numb to the idea. This is coming from an environmentalist.
That said, there were a bunch of things that bothered me that PROBABLY wouldn't bother most people. Like why there were African Black-footed Penguins (Africa) and Little Blue Penguins (Australia and New Zealand) living with the Adeles? Or why Mumble is still fuzzy after having almost lost all his down in the first movie. Or why Eric has all of the same markings as his father and is the ONLY blue-eyed penguin aside from his father. Is he retarded too? Did they just run out of character design ideas?
All of this, plus the plot not really picking up until about a third of the way through the movie, bothered me... but it was kinda okay. Again, the visuals were great and I very much enjoyed the music. The penguins and other animals were fun to watch and for the most part realistic. I was dancing along to the big dance numbers and thought the reveal of Erik's talent was awesome (even if it sounded like an opera singer inhaling helium).
So, sure, if you want something energetic and cute to sit your kids down in front of, be my guest. I might even watch it again, if I can get around the dead plot and nature issues. It's fun and pretty to look at. Just shows what a superficial, visual race we are.