This is an excellent teaching tool for Chinese. It teaches you the Mandarin dialect (the official language of both China and Taiwan), pinyin (the anglicized pronounciation guide) and the simplified Chinese writing system (used in China).
Each lesson has a few characters and phrases to learn. You can hear the program pronounce each character and phrase, speak into the Nintendo DS to compare your pronounciation to the program, and practice writing. There are also games to play to strengthen the learning process. You can repeat the lessons and games as often as you like.
With Chinese writing, a character is only considered to be written correctly if the strokes are written in the right order and direction (imagine yourself writing a "plus" sign, there are 2 strokes that can come in different directions). So I found the writing part, using the stylus to write the characters, particularly helpful, because I could practice writing the characters.
A huge bonus is the mini-program included that includes travel phrases, dictionary of words known, etc. So if I'm in a restaurant in Beijing, I can choose the dining phrase from the list and show it to the waitor to ask a question.
I've tried to learn Chinese from language CDs, but found it hard to use because the CD's go on their own pace and the pronounciation is very fast. With this program, I can choose to replay something over and over again. With books, I'm not sure if my pronounciation is right. With this program, I can tell easily with the DS' audio capabilities.
So basically, this is the best language teaching tool I've seen for Mandarin (short of moving to China or knowing someone who speaks it fluently.)