まずい Bad-tasting for any reason. The opposite of おいしい.   $$$
っぱい(すっぱい) Sour, acidic flavor:lemons, vinegar, pickled plums.
(にがい) Bitter. Medicine, okra. Can also be used figuratively – the bitter taste of defeat.
(しぶい) A really arbitrary word for a flavor that only Japanese people seem to be able to taste. It means bitter, kind of. But it’s only used about unripe fruit, too-strong green tea, or certain species of raw persimmon. However, usually it’s used figuratively, to mean “cool older guy like George Clooney or Kiefer Sutherland.” Which only adds to the confusion.