Absinthe is illegal in the US if it contains wormwood (thujone i believe is the chemical contained in wormwood which is supposed to be toxic)
Typically you should drink it with water and sugar, it takes part of the bitterness away.. look up absinthe spoon, and you will see what I am talking about. It's a slotted spoon that you put sugar cubes on and then pour the water over it to dissolve the cube.
It is different than say everclear because of the effects of the herbs contained in the drink, where everclear is almost pure grain alcohol, you only get an alcohol effect. With absinthe you get the effect of the herbs as well. Typically absinthe is anywhere from 55% to 80% alcohol. If you are going to europe you can find absinthe, but they only contain a small amount of wormwood, not what the traditional recipe calls for, and for the most part contain wormwood oil and not the actually plant. Which, is said to not have the same effect.