When I look at a sequence of content, I want to feel that it is going somewhere. A strong first line makes me curious. The next page needs to give me a reason to keep reading.
I have given this feedback before: the first page should draw people in, and the following pages should gradually explain or reveal the idea. If every page is another isolated headline, the story never develops.
Give the next page a job.
It might answer a question, add a detail, or change the way we understand the opening. Each piece should bring something to the sequence. Otherwise, we are asking for attention without giving much back.
The same applies to the relationship between words and images. I want the writing to have enough depth to carry an idea, and the visual to make that idea easier to enter.
That is what I look for when a draft feels flat: a reason for one thought to lead to the next.