expression, noun-modifying (irregular)
exceeding what one had heard; beyond expectations
Set phrase used when something is even more impressive, beautiful, or terrible than one had heard beforehand. Often modifies a noun.
富士山は聞きしに勝る美しさだった。
Mt. Fuji was more beautiful than I had heard.
その映画は聞きしに勝る面白さだ。
That movie is more interesting than I had heard.
Similar meaning 'just as rumored', but 聞きしに勝る emphasizes exceeding the reputation, while 噂に違わぬ means living up to it.
From classical Japanese 聞きし (attributive form of 聞く 'hear' + past auxiliary き) + に + 勝る 'surpass'. Literally 'surpasses what one heard'.