Hazel is just full of opinionated treasures. Hazel is quick-witted, well-spoken, and snarky to boot. Take her thoughts on the Encouragements scattered all around Augustus' house:
This is an old argument in the field of Thinking About Suffering, and its stupidity and lack of sophistication could be plumbed for centuries, but suffice it to say that the existence of broccoli does not in any way affect the taste of chocolate... "A lovely thought." (2.97)
Not only does this passage showcase her witty turns of phrase, it also gives us an idea of why she talks like she does, why she tells it like it is. Hazel obviously thinks that trite phrases (like the Encouragements) are just stupid. That means you can be sure she'll never write like that. And we don't know about you, but we much prefer snarky to trite.
Plus, Hazel's writing is easy to follow because it's written in a conversational way; as if we're sitting down talking to a close friend. And that makes us feel like we really know Hazel.