There are many things to be said about green tea... but nothing is more important to talk about than the correct way to prepare it.
I know many people who are averse to green tea because they've been exposed to a wrongly-brewed cup. You see, when you purchase green tea at your local supermarket, the instructions on it tell you to pour boiling water over the tea bag. If you indeed do that the first time you purchase green tea, you will have tremendously cheated yourself. Why is that? Because green tea needs to be made with hot but not boiling water.
Whenever you make a cup, you should mix the boiling water that comes out of the tea kettle with a little bit of cold water. And then pour this cooler mix on your tea bag or tea leaves
Doing otherwise is akin to treating yourself to a poisonous tea. First of all, it will taste horribly.
If you choose to go with the boiling water, you're gonna come with a disgustingly bitter brew. It's so putrid that someone accurately likened the taste to that famous light-colored liquid in the toilet bowl.
Second, not only will it taste bad but might also make you feel a little bit sick. The boiling water burns the leaves and the resulting brew becomes somewhat acidic, which might give the person drinking it a stomachache.
Another negative health implication is that it causes a rapid drop of blood sugar and makes you feel very hungry. Even when it is prepared with the right water temperature, green tea midly lowers the blood sugar, which makes it the perfect drink after a heavy meal. But the boiling water makes the chemicals in the tea more potent, hence the blood sugar drop that results is very sudden and may cause urgent hunger. Of course, people's bodies do not respond as my own, so they may deal with it better than I do. While I get incredibly hungry as a result, other people might get only mildly hungry.
Incidentally most coffeeshops are guilty of bad green tea preparation. Some small coffee/tea shops do brew green tea with the right temperature, but the large national chains like Starbucks and Dunkin Donuts tend to make it with the same boiling water they use with the rest of their teas. That's why the best bet for aspiring green tea drinkers is to make it at home.