разочаровывающий – English translation

all sizzle and no steak (о событии или человеке Fyrvaktare)

dusty; not all it's cracked up to be (SirReal)

disappointing (oleg.vigodsky)

disappoint; disenchant; disillusion; let down; chagrin; sophisticate; balk; disillusionize; disaffect (someone bigmaxus); underwhelm (MichaelBurov); chill; deflate; burst one's bubble (КГА); bum out (To sadden one or cause one to feel disappointed. In this usage, a noun or pronoun can be used between "bum" and "out." : I can't watch the news because it always bums me out vogeler); disabuse; uncharm; undeceive; unspell

let the side down (окружающих своим поведением; to behave badly or do something that embarrasses or disappoints your family, friends etc Sonora)

rain on someone's parade (VLZ_58)

deceive (преим.)