Sentence question

[Alissa Nesson]

Question for you guys about this sentence:

This book is captivating historical fiction.

Is this wrong? Should it be:

This book is a captivating historical fiction.

Thanks for any feedback on this

[Tobi Adefila]

I will go for the second option

[Alissa Nesson]

But is the first one a grammatical error or does it just not sound as good? AI says both are grammatically correct but the second option is smoother.