Having just seen Surf's Up, I was struck by the nature of conflict in the film compared to Ratatouille. Both films have animals who are obsessed with something and that obsession brings them into conflict with those around them. While I enjoyed Surf's Up, the nature of the conflict in that film is much less compelling than in Ratatouille and I think that is one reason for the film's relative failure at the box office. To date, Ratatouille has earned $206 million domestically while Surf's Up has earned under $59 million. Surf's Up also did significantly poorer than Sony's first cgi feature Open Season, which grossed $85 million.
The key issue is how much danger the character's objective creates. In Ratatouille, Remy's urge to cook great meals puts him in mortal danger from humans. The woman who owns the country cottage uses a gun against the rats and Linguini is charged with drowning Remy when he is caught in the kitchen. Furthermore, Remy's desire to cook brings him into conflict with is own family. His father refuses to believe that humans will ever accept rats and it causes a rift between them.
In Surf's Up, Cody's jeopardy is at a much lower level. His desire to surf may annoy his mother and brother, but there is no threat to any of them or their relationship as a result. His desire to win the surfing competition puts him in danger with regard to the ocean, but poses no threat to the wider community.
In Ratatouille, we learn that Remy is a genius cook, but in Surf's Up, we learn that Cody has an unrealistic view of his abilities, so while we root for Remy to overcome obstacles, we know that Cody has to fail before he can succeed. This reduces the tension as the initial failure is inevitable.
The genius of Ratatouille is that the basic situation -- a rat who wants to prepare human food -- immediately puts Remy in conflict with everybody around him. For Remy to succeed, he literally has to change the world, changing the rat perspective on people and the human perspective on rats. The weakness of Surf's Up is that for Cody to succeed, he only has to change himself. The external conflicts he faces are mild and the stakes are low.
Ratatouille relates everything in the film to the central conflict. The question of Linguini's parentage and the ownership of the restaurant don't concern Remy directly but still have an impact on Remy's objective. The business in Surf's Up with Chicken Joe and the aboriginal penguins is a comedic detour that produces laughs but doesn't contribute to the conflict.
Surf's Up is worth watching. Tom Sito and Keith Lango both have good things to say about it. Lango points out the high quality of the acting and I agree. While it's probably wrong to use the word "naturalistic" with regard to surfing penguins, the truth is that the acting is believable and subtle. It doesn't call attention to itself, yet it's as expressive as the voice work, which is of a high quality.
However, dramatic conflict is the mainspring that powers a movie and the danger is that low-key conflict results in a lack of audience enthusiasm.