This is the 155th most frequent Ukrainian word.
такий
"Such," "this kind of," or "like this."
Here, "такий" is used to express the characteristics of the person, specifically to emphasize 'how interesting' he is as a teacher.
Він такий цікавий учитель.
He is such an interesting teacher.
Here, "такого" modifies "величезного будинку" to indicate the degree of its size, emphasizing that it is extraordinary.
Я ще не бачила такого величезного будинку.
I have never seen such a huge house.
Here, "таким" functions as a comparative term, paired with "недоуком" to underline the nature of the behavior.