Is it a good academic practice to tell the reader in the introduction what the essay is about directly? Is it academic to tell the reader in the introduction what the essay is about directly?

For example, after some introductory ideas, you tell the the reader this essay or section discusses so and so.

Or should the writer end the introduction with the thesis statement that indirectly tells the reader what the essay is about?
I'm not sure what you mean by "essay", but for an academic paper in general, the reader should be told a minimum of four times what the paper is about and what your contribution is. This should be stated in (1) the title, (2) the abstract, (3) the introduction, and (4) the conclusion.

That is a typical North American style. In some academic cultures, such as Northern Europe where I'm sitting, it's common to not do any of that. In a typical paper here, you can read all of the four parts mentioned above and still have no idea what the author is bringing to the table. You're guaranteed to annoy many readers that way.

So my answer to your question is: Tell the reader as soon as possible what the point and punchline of your paper is. The reader doesn't want a mystery novel, he wants to know as soon as possible whether your paper is worth reading.