Common misconception about wasabi is people think wasabi is Japanese horseradish. It is completely wrong! Wasabi is actually the gratings from the roots of the wasabi plant.

Unforunately, in a lot of the places you are being served imitation wasabi.

But real wasabi is really expensive. You have to pay probably 3-4 dollars for 1 wasabi plant which might only be able to serve 2-3 people in such amount. Not to mention it is hard to find in the US and you have to buy and serve it fresh. Real wasabi should look like the profile picture, it should look like some gratings from a yellowish green plant, but not the solid translucent green that you see everywhere in all sushi restaraurants.  Real wasabi don’t taste that spicy or pungent to the nose (those are effects from the mustard in imitated wasbi paste), but  a rather mild with a pleasant minty after taste.

Most of the wasabi you see are fake. Probably you should grate your own wasabi from the market if you really want to try. You can buy them in Japanese Supermarkets. Nijiya Markets in the West Coast sells them, at a highly inflated price!

THIS is wasabi: