WordNet sense 1 (lacking taste or flavor or tang):

bland, flat, flavorless, vapid, flavourless, savorless, savourless

WordNet sense 2 (lacking flavor):

tasteless

WordNet sense 3 (not injurious to physical or mental health):

harmless, innocuous

WordNet sense 4 (lacking interest or significance):

jejune

WordNet sense 5 (arousing no interest or attention or curiosity or excitement):

uninteresting

WordNet sense 6 (not appetizing in appearance, aroma, or taste):

unappetising