From London to Tokyo by train (where possible) and back through Siberia - it's one hell of a journey, and sometimes it feels like it. The latter chapters especially are written in a kind of "Oh, let's get this over with" style, and you don't learn much about either Russia or Russians, except that there's so much snow and cold it drives everyone to drink. The earlier chapters are more enjoyable, and his account of Japan's sex and death fascination is quite an insight. The chapters on Vietnam and India are also enjoyable, and you have the impression that he wasn't as bored and lonely in these places as he becomes later.
Although this book was written in 1975, there are very few references to contemporary events, so I didn't have the feeling (reading it in 2002) that it was nearly thirty years old. No doubt everything has changed since then, and I'd like to read a more up to date account of the trip. Having read quite a few of Theroux's travelogues, I think he's mellowed with age and maybe if he went the other way 'round next time, London - Moscow - Tokyo - Calcutta - Kabul, he'd be kinder to many of those that he meets. Of course, it wouldn't be quite as entertaining then!