Well, what do you expect from a book that describes God's creations as "very cool. They were very cool, but they didn't work" (6.1)?
Even though these are some heavy subjects, Rosoff keeps the tone light—even the most well known books of the Bible become punch lines. Like that rewriting of Genesis:
In the beginning, the earth was without form, and void and the darkness was upon the face of the deep. And the spirit of God moved upon the face of the waters. And God said, 'Let there be light,' and there was light. Only it wasn't very good light. Bob created fireworks, sparklers and neon tubes that circled the globe like weird tangled rainbows. […] Bob thought his creations were very cool. They were very cool, but they didn't work. (6.1)
Rosoff also likes to make tongue-in-cheek jokes, mostly about Bob being God. For example, "Bob had lost interest—he was gazing, fascinated, at the brightly graffitied wall of an old brick warehouse as the felucca drifted slowly past. On it was written: THERE IS NO GOD" (36.37).
LOL, right? See, the person who scrawled this thinks that there's God because of all the horrible weather and suffering that's been going on. But we know that it's all happening because of God/Bob.
Along with all of her comedy, Rosoff sneaks in some seriousness. She's empathetic even to the most horrible of the characters. Even Bob. She writes,
For whole moments at a time, you could almost feel sorry for him. He did look lost. And if (by some quirk of fate) Mr. B happened to be in the mood to notice, he could see the isolation that enveloped Bob like a shroud, and the sadness too. (12.60)
Poor Bob, right? These moments help us see that maybe the story isn't as simple as we first expected it to be. It helps to make even immortal characters more human.