The thing that Cars spawned got bored with itself after one movie. And who can blame it? It was Cars with planes. And less personality. And less imaginative animation. And less of every single other thing you'd want in a film. I can only guess that the makers, stumped for ways to create sparks from Yet Another Championship Race, endured several rounds of soul searching and frustrating concept meetings. How to boost kindergarden brand loyalty for Dusty Crophopper (voice of Dane Cook)?
Easy. Turn him into a flying firefighter, that's how. And it sort of works.
Dusty, suffering from engine obsolescence, realizes that his days as a not-especially-interesting racing plane are over. In his subsequent depression he realizes that the best response to this challenge is to become a meaningful contributor to society, so he employs his skillfull flying in the service of his local fire department. He trains hard to do it and then he does it.
From a what-are-we-supposed-to-do-with-this-franchise perspective, this was a briliant move. Suddenly there are awesome (and kind of frightening) fires to animate. Suddenly other talking planes and talking cars need rescuing from awesome fires. Suddenly there are stakes involved if those talking planes and talking cars get burned up in an awesome fire. Dusty has a purpose, dangers to brave, other characters to save. There's very little downside.
Unless you count flat-ish, underdeveloped characters and only occasionally funny dialogue, that is. Call it the curse of low expectations, but this is the sequel to a spin-off that was never meant to be in movie theaters in the first place. Kids will enjoy it regardless, so their satisfaction is already beside the point.
It's a series that's trying harder when it doesn't have to, figuring out a way to keep its own creatives interested in coming to work each day, and that counts for something, especially when it comes to fabricating a finished product that needs to fuel the merch engine. This sort of thing could also very easily, if executed improperly, test the threshold of adult ticketbuyer boredom. That it doesn't do that isn't a miracle of cinema, but it may feel like one for its duration.