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.
There are many ways to structure an introduction. However, in the context of psychology I am familiar with the two broad approaches you mention to writing an introduction.
In psychology, students are often taught to write lab reports using an hour glass structure where they start broad and then narrow in gradually into stating aims and hypotheses at the end of the introduction. This structure can really annoying to read, because the purpose of the paper is not immediately clear.
Personally, I prefer the opening-body-currentstudy structure for an introduction. Specifically, the opening section of the introduction contains around three paragraphs that cover the importance of the work, a little context, a little bit of the gap, and importantly the aims of the paper. The introduction then reviews relevant literature, and culminates in a statement of a brief description of the current study (see here for a little more discussion). Thus, in the opening few paragraphs, you might have a paragraph that begins: "The purpose of this paper is..."
The general principle is: Make it easy for the reviewer/reader to see what is the novel contribution of the paper.
