If you've ever had Pernod, much like that. If not, then kind of like liquorice in booze form.

The important thing about absinthe is that it's exceedingly strongly flavoured, which means it covers up the taste of really cheap and nasty spirits. Hence Degas painting some down and out alcoholics, who's illness is enabled by the cheap bottles of green fairy. Admittedly, he does that very well - it's a great painting.