I lived there for 2 years.
Negatives:
Very strict and retarded rules, combined with autistically rule-abiding citizens.
No spontaneity, everyone has agendas and plans.
Work and consumer habits are people's identity. The consumerist NPC drone worker stereotype is real.
Tatemae/Honne. People won't tell you if they dislike something about you, they'll just treat you worse and talk behind your back. This is especially true as a foreigner.
Japanese people are hard to befriend, especially as a foreigner.
Positives:
Politics are very private. Japanese people generally seem indifferent to it. Barely any demonstrations or protests.
Japanese people are very well-behaved. Even the poorest Japanese carry themselves with a level of dignity and discipline that's all but vanished from the Western lower class.
Beautiful cities. Tokyo truly feels alive compared to European capitals. Also, nice countryside and nature.
Things work, streets are clean, food/restaurants are nice and cheap.
Overall it's a nice country, much better than Europe in many aspects, but it can be difficult as a foreigner.