My top five good things about living in Japan:
1) I really like the way the cities are laid out. You can walk or ride a bicycle just about anywhere, unlike in North America where the cities are so spread out you can't get anywhere without a car.
2) I love Japanese history and the large number of beautiful temples, castles, machiya, gardens and shrines that are scattered throughout the country. Nothing like that where I come from.
3) I like the countryside. Very laid back feel, lots of attractive mountains and ricefields.
4) I like the social life -karaoke, Izakaya, etc.
5) Sports - I'm a huge sumo and Japanese baseball fan.

Top 5 bad things about living in Japan:

1) The concrete everywhere, especially on riverbanks and shorelines, is just really really ugly
2) The downside of living in convenient, compact cities is that you have to live in a tiny apartment, and you also have to deal with all the noise...
3) The apartments are really cold in the winter. I used to have to lug this gas heater (which I had to manually refill everyday) around from room to room just to keep warm. I'm from Ottawa, where the winters are way worse, but the homes are way better heated.
4) It really bothered me whenever I saw some attractive old building being demolished to make way for some eyesore, which seems to happen on a daily basis.
5) The lack of trees in the cities.

One thing I wasn't sure which list to put on was my relationship, as a foreigner, with Japanese people in social settings. On the one hand as a foreigner you aren't really subject to the rigid social norms (which is a plus), but on the other hand you get treated like a baby sometimes ("Wow, you can use chopsticks??!!"), which used to rub me the wrong way. So I would say that is a neutral point.