Visiting Japan for a Month

Hi Guys!

My partner and I are visiting Japan for a month, and leaving in a couple of weeks. I was just wondering from those of you who have been there before...what did you absolutely love about it? What was on your must see/do? Whenever I travel I always end up finding ten million things i want to check out 'next time'. Was there anything that surprised you that you would definitely want to do on your next trip? i've read all of the forums online I just really prefer to get fellow travellers opinions. Thanks!