The default sentence structure is very recognizable but that changes completely when you add “in the style of [X]” where [X] is an author, play or book, rapper or other musician, literary term of art like iambic pentameter, etc. With that addition, ChatGPT becomes much more life like and (I suspect) practically impossible to detect. Throw in a little human editing and curation and… ruh roh.
How would you build a ChatGPT detector? Frame it as a dirty limerick.
There once was a ChatGPT detector,
Built to detect bots and protect her,
She'd scan for reply,
And then with a cry,
Say "That's not human, rejector!".