Synonyms for Unappreciated (same or very similar meaning)
WordNet sense 1 (not likely to be rewarded):
thankless, ungratifyingWordNet sense 2 (not rewarding; not providing personal satisfaction):
unrewardingWordNet sense 3 (having value that is not acknowledged):
unsung, unvaluedWordNet sense 4 (not recognized or admitted):
unacknowledgedFrom the ODE community, based on WordNetadd/edit