I went to Japan in January but only for 2 days, we stopped there before going to Canada and America.
Japan is awesome I loved it and will definitely be going back. I recommend going to Shibuya. We spent most of our two days shopping here, however its mainly the fashion area so clothes, shoes etc only found one electronics shop. Still you must go there is a road right near the station that gets sooo packed when people cross, I think its famous for it.
Also make sure you plan where your going because it is so massive. We tried to find electronic shops with no luck. There is a district for technology but seeing as there city loop was like 30 stations we didn't quite have enough time to find it.