I've been learning japanese (and living in japan) for the past few months, and tried out duolingos new course when they released it yesterday. I've used quite a few different apps and books, and I must say I was pretty unimpressed. Their lessons give very little info on what you're learning, and with things like kanji it only teaches you the sound and not the meaning. I will experiment with it a bit more, but I've already done the first 6 or 7 lessons (chapters?) and am not impressed.
If you want to see an incredibly well built japanese learning tool, look at Human Japanese http://www.humanjapanese.com/ - i am in no way affiliated, just a happy student
If you want to see an incredibly well built japanese learning tool, look at Human Japanese http://www.humanjapanese.com/ - i am in no way affiliated, just a happy student