For starters, it's a Cars clone - right down to the rookie main character, the mentor with the dark secret, the exotic romantic interest, goofy sidekick and conniving villain racer. It's so obviously copied that I'm guessing it was an intentional business decision - to make a safe 90 minute commercial for a new range of toys - which is all it is. Anyway, Dusty, the main character, didn't have a character arc - which killed the story completely for me. He was a nice-guy rookie character at the start and was the same nice guy at the end. In contrast, what made Cars entertaining, and what drove the story, was Lightening McQueen's transformation from arrogant upstart as he "came of age" and emerged a more mature, empathetic character in the end.
The other film that suffered the same fate was Despicable Me 2. The first Despicable Me was great! One of my favourites and fresh change from the Pixar and Dreamworks stuff. The story was driven by Gru's torturous internal conflict as he transformed from super villain to doting dad. Unfortunately anything resembling a character arc in Despicable Me 2 was absent - doting dad at the start and doting dad at the end. If not for the funny minion actics holding the film together, it would have been a complete dud.