On the third movie, I met the saber-toothed squirrel, Scrat, and his adventure with his beloved acorn. The story seems to be almost incongrous with the rest of the plot and I really found him a peeve.
In this 4th movie though, I think the scriptwriters were able to make good use of his character. They were able to bring a message too. Scrat is just a simple squirrel who is just trying to find a place for his acorn, and by doing so accidentally caused the continental drift, unbeknownst to him. This is a message that says your actions have an effect on others, directly or indirectly, and whether you know it or not.
Let's not forget Diego. He was the thing I'd been wanting to see since the start of the movie. Denis Leary's voice adds up to his charm. This sabertooth tiger sure is a loyal friend of Manny and Sid, imagine his patience for Sid and Granny.
This ice age is surely a treat.