One reason to study Japanese (or Chinese or Korean or Guugu Yimithirr) it seemed to me was that because we think in a language, our language affects what we think. You have one picture of reality when you think in English, another when you think in Japanese. And because Japanese is so different from English, it expands what you can possibly know. My analogy would be the difference between my walking through the woods or walking with a trained botanist who can identify all the plants and trees. It would be a much richer experience with someone who knows the language.
Guy Deutscher, an honorary Research Fellow at the School of Languages, Linguistics and Cultures in the University of Manchester, has written Through the Language Glass: Why the World Looks Different in Other Languages, which explores these questions. I found it fascinating, although if you read the article in the New York Times Magazine, "Does Your Language Shape How You Think?" you have most of the book's meat.
Yes, language does shape how you think, but not in the way that linguists had thought. Just because a language does not have a future tense, for example, does not mean that native speakers cannot imagine the future. Just because a language does not have plurals (Japanese has almost none) does not mean that native speakers cannot distinguish between one book and five books. Your language determines not what you can say, but what you must say.
For example, I cannot talk about my "brother" in Japanese; I must talk about either my "older brother" (ani) or "younger brother" (ototo); there is no single word for a male sibling. Similarly, I cannot say "I went out with a friend," in Italian without identifying the sex of the friend (amico or amica).
Deutscher's book is an interesting account of the intellectual debate over these issues. It does seem clear that our language colors our reality. (And color words are particularly troublesome for linguists: Did Homer really see world in black and white because there are no color words in the Illiad and the Odyssey? What color is a wine-dark sea?) The book is filled with interesting facts about languages. German, for example, has seven ways to form a plural. Speakers of certain Aboriginal Australian languages do not talk about something in "front" of you or "behind" you, but to the north or the south, which changes as you move through space; as a result these people seem to always know which way is north.
I would recommend the book to anyone who has more than a passing interest in language. I would recommend the Times Magazine article to those who have only a passing interest.