Airman, has a slight Scottish accent, and I am sure I would not have enjoyed the book nearly so much without his delightful voice.
Airman has all the components necessary for a fantastically fun adventure story: our protagonist, Conor Broekhart, is born in a hot air balloon while being shot at from below; he spends his boyhood studying the science of flight with a Frenchman; he's cruelly betrayed by a man named Bonvilain (what a fantastic name) and sent to a prison island where he toils away in the salt mines; and eventually...well, you can probably guess. And of course, there's a bit of romance, which any respectable adventure tale should have.
The story is set in the fictional nation of the Saltee Islands in the late 1800s, which gives Colfer leave to do pretty much whatever he wants regarding the royal family and battles and such, without worrying about messing with history. Is that cheating? Well...yes, but it's forgivable. Airman isn't meant to be a book that reveals Great Truths About Humanity - it's a hugely fun story with funny, interesting characters and non-stop action.
While Keating does not have the vocal range of either Jim Dale or Barbara Rosenblat, my top two audiobook narrators, he does a solid job of differentiating the characters, particularly Bonvilain and Conor's guard on Little Saltee. There are only a handful of really major characters, so it's easy to keep them straight, and Keating has a really authentic way with all the required accents (English, French, and American, plus the Scottish narration).
Colfer must have had so much fun writing this book. I've heard it compared to The Princess Bride due to its combination of adventure and camp, and I'd say that's a fair judgment. It's not a book to be taken too seriously, and as an audio, it's a joy.