I finally got to try Gyokuro green tea at a beautiful little salon de thé called The Tea Caddy, in the Latin Quarter of Paris. It is never a cheap tea, but they had it for around half the price I've seen elsewhere.

The leaves and the infusion are remarkably green, quite vividly so, and if you can imagine it, the taste is, too - quite richly vegetal, but not unpleasantly so. It is also a very characteristically Japanese flavour, with the seasidey overtones that implies. It's not quite right to say that they're fishy, but there's certainly something of the ocean to Japanese green teas, which some people dislike.

For my part I found the Gyokuro delicious, with a particularly deep flavour and very little bitterness to it. It stands up well to multiple brewings, at least as many as I could fit in on my visit.

Gyokuro is made from tea that is shaded for the last few weeks of growing, deepening both colour and flavour, adding to the theanine and caffeine content. This is also how they make Matcha, the powdered tea used in the Japanese tea ceremony cha-no-yu, although the drying process differs.

Gyokuro should be brewed with cooler water than most green teas, only 50-60°C, and far more tea per cup - two tablespoons for just a quarter-pint of tea! The taste and the rebrewability should make up for the apparent lack of economy.

With thanks to O-Cha.com and Wikipedia for some details.
This writeup with pictures: http://oolong.co.uk/oo/?p=14