Green tea is tea that has been dried out quickly to stop it from oxidising and turning black. The best green teas, like sencha, are steamed to break down the cell structure of the leaves and let the moisture out gently; cheaper green teas are dried by being heated in pans. Green tea brewed correctly has about one third of the caffeine of black tea, and significantly greater quantities of various antioxidants; oolong tea lies in between the two on both counts. The taste of green tea bears little resemblance to that of black tea, although it does share a little of its astringency and just a hint of bitterness. The experience of drinking green tea is dominated more by the aroma than by its effect on the taste buds - good green tea has a fresh, leafy, grassy aroma. Teas like gunpowder green have overtones of smoke in their scent, while Japanese teas like sencha often carry a hint of sea air.
Green tea is consumed frequently throughout most of the Far East, as well as the Middle East and north Africa; where most of us in the West will drink cups of water, the Chinese and Japanese are more likely to have green tea of one kind or another, a custom which probably started when people were boiling water for hygiene reasons and realised they could make it taste a whole lot better with a few camellia sinensis leaves. Besides tasting pretty good, green tea has long had a reputation for bringing tremendous health benefits, and is especially recommended for the ill. Modern science has backed up traditional beliefs in the tea's power to promote well-being; as Accipiter relates above, green tea has been shown to have a wide range of health benefits. It is also said to help with weight loss, and to boost female fertility.
In Japan, green tea has inspired a way of being, chado, centred around the appreciation of tea and other small pleasures. As Kakuzo Okakura puts it in The Book of Tea, 'Teaism is Taoism in disguise': a gentle absorption in the immediate facts of living; a steady awareness of the things which make existence worthwhile. The Japanese Tea Ceremony, performed with little change for the last five hundred years, remains a prominent feature of the country's cultural life.
Although many people enjoy it straight away, and others grow to love it, the vegetative flavour of standard green tea is not to everyone's taste; for those who don't much like it, and indeed those who do, several variants are worth exploring. Hojicha is green tea which has been roasted to bring out a delicious toasty flavour with a hint of caramel; it has quite a bit less caffeine than sencha. Kukicha is quite similar, being made with the roasted twigs of the tea plant; it has even less caffeine, and a slightly sweeter, earthier flavour. Green tea is also available flavoured with mint, various fruits, jasmine flowers, or roasted rice. Green tea with roasted rice is what the Japanese call genmai-cha and the Koreans call hyun-mi-nok-cha; its taste is dominated by the savoury, toasted flavour of rice tea. Oolong tea - tea which has been only partially oxidised, making it a close relative of green tea - has many of the same health benefits, and a completely different taste without the leafiness of green tea; if you like the sound of green tea, oolong is certainly worth a try too.
But then, I would say that...
Kinds of Green tea:
(not intended to be an exhaustive list)
* This tea is not noded yet. I will get round to longjing and Tai Ping Monkey King sooner or later, and Young Hyson once I find anywhere to buy it.