The Good: very safe country; Tokyo is an amazing city; public transportation is extensive and fairly cheap (no need to have a car); good, inexpensive food; no tipping; if you are a straight guy, dating will be somewhat easier than in Silicon Valley.
The Bad: as Robert says, working at Japanese companies can be soul-crushing; IT salaries are much lower than in comparable US areas; foreign web/software companies' presence here is very small in terms of R&D; rent in Tokyo is expensive; jobs that use English or otherwise hire foreigners are extremely concentrated in Tokyo; most Japanese cannot speak English, you need to learn Japanese; Japanese is not easy; many train lines in Tokyo are somewhat crowded.
The Ugly: Tokyo is ugly; you cannot easily get permanent residence even if you're married to a Japanese person, has a job and have lived here for years; most tenants refuse to rent to foreigners (discrimination is not illegal); we are subject to somewhat big earthquakes.
> if you are a straight guy, dating will be somewhat easier than in Silicon Valley.
Only "somewhat"? Haven't you read Charisma Man? Dating in Japan is like paradise for a nerd if you like Asian women. Actually, even Caucasian women are easier to get in Japan because you'll have no competition because all the other Caucasian guys will be with Japanese women.
The rent situation is accurate, in that discrimination is not illegal. On the other hand, it is definitely not something that prevents you from getting a decent place full stop, by any means. And none of my married (to Japanese) friends report any trouble at all, for that matter. And permanent residence is certainly on the table if you've been here long enough.
The dating scene is awful though, don't let anyone tell you different :-)
The Bad: as Robert says, working at Japanese companies can be soul-crushing; IT salaries are much lower than in comparable US areas; foreign web/software companies' presence here is very small in terms of R&D; rent in Tokyo is expensive; jobs that use English or otherwise hire foreigners are extremely concentrated in Tokyo; most Japanese cannot speak English, you need to learn Japanese; Japanese is not easy; many train lines in Tokyo are somewhat crowded.
The Ugly: Tokyo is ugly; you cannot easily get permanent residence even if you're married to a Japanese person, has a job and have lived here for years; most tenants refuse to rent to foreigners (discrimination is not illegal); we are subject to somewhat big earthquakes.