I've lived in Japan for 8 months. As much as a I loved it, It wasn't easy. But definitely worth it.

The first thing I'd say about going there is don't expect the perfect utopia that is often depicted by the media and dreamed of by over-excited anime fans. It's not as perfect and care-free as it seems. Even though the Japanese are generally very welcoming to outsiders, this can change if you tread on their toes and become a nuisance in some way. Furthermore, as has been pointed out, people work very hard and the suicide rates are high.

But I wouldn't want to put people off going. It's a wonderful country and not just because a lot of our favourite stuff comes from there. There's a wonderful blend of tradition and technology, beautiful scenery and a really nice sense of community.

As for language, you're fine if you're in Tokyo and you don't speak Japanese. There's plenty of staff at tourist attractions and restaurants who can speak English. Though if like me you do speak Japanese, you'll find it difficult to practise when they see that you're foreign and immediately speak to you in English! But they're just trying to be accomodating, so it's all cool.

However, outside Tokyo, speaking Japanese does help. It's harder to find an English speaker where you need one, though if you stand around in a train station looking confused for long enough the chances are an English speaker will find you and offer you some assistance. The Japanese are really helpful. Younger people are more likely to speak some level of English than older people, as English has become compulsory at earlier stages of education in recent years.

Finally, think carefully about what you do. There are big cultural differences about even the tiniest of things. Taking your shoes off at the door is REALLY important. Don't eat on the street. These may seem like insignificant things in the west but if you don't respect cultural norms you offend them and furthermore make other foreigners look bad. So learn about these cultural differences before you go.

Hope that helps, if you're thinking about visiting Japan