WordNet sense 1 (damaged by decay; hence unsound and useless):

decayed, rotted

WordNet sense 2 (not in good condition; damaged or decayed):

unsound

WordNet sense 3 (very bad):

crappy, icky, lousy, shitty, stinking, stinky

WordNet sense 4 (having undesirable or negative qualities):

bad

WordNet sense 5 (in an advanced state of decomposition and having a foul odor):

putrid

WordNet sense 6 (touched by rot or decay):

corrupt, tainted