This is not the first thread on the subject (see also this one and another about living in Japan vs US), but I'd like to start something fresh, and get something that does not degenerate in offtopic arguments, So the rules for this thread are :
1) write a "pros" paragraph/list and a "cons" paragraph/list.
2) do not argue about other people's point of view about other countries than Japan (so if someone says Tokyo is safe, and another one says it is dangerous, let's just assume that they come from different societies, and there is no "right answer", just personal opinions).
3) keep it concise. No need to write an article to explain each point.
4) the title says "Tokyo" to make it easier, as saying that Japan is a convenient place to live would not have much meaning in a village in Shimane or Akita prefecture, although it does in big cities, esp. Tokyo. Likewise, saying that winters are mild is fine for Tokyo, but doesn't make sense for Hokkaido.
5) I wrote "as a foreigner" because most people on this forum aren't Japanese, and their point of view regarding lifestyle can be very different. But Japanese are welcome to post too.

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Pros

Food & Climate

- the climate is mild and clear in winter, and it doesn't rain much compared to Northern Europe.
- the food varied, tasty and cheap by Western standard

Convenience

- very convenient for shopping, buying food, etc. thanks to the numerous "combini", restaurants, department stores, etc.
- Bicyles can drive on the pavement/sidewalk or on the road (convenient for bikers, although some will find it dangerous)
- trains are spacious (high ceiling and wide) and in good condition (no graffiti, quite new...)
- easy to find a job for Westerners (although not any job)
- latest mobile phone technology readily available

Socio-cultural system

- the safety in general
- the service and attention to customers in most places in excellent
- the respect and politeness of most Japanese people have for others (except for noise)
- low taxes (esp. consumption tax)


Cons

Climate

- summers are too muggy

Cost of life

- domestic flights, shinkansen and taxis are all very much overpriced
- cars (including licence, annual check, highway fees...) and parking spaces are too expensive
- no buses or trains running from about 00:30am to 5:00am. (no nightbus system and taxis are expensive)
- houses/apartments are poor quality and expensive
- cinemas are expensive

Socio-cultural system

- the police has the right to arrest anybody for 23 days without evidence and refuse them to contact a lawyer or their family during that time (scary, especially as foreigners are more likely to be suspected of any crime than Japanese)
- foreigners are foreigners and will always be regarded as such, stared or pointed at by kids, or refused entry to some establishments.
- bad education system (problem for people having children in Japan, and do not want to pay a fortune for a private international school)