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Critical Backlash. It literally says so on that page.
Unless you meant opposite on both attributes (no hype, very high quality), which would be Cult Classic or Needs More Love.
Edited by KD
Definitely a case where there's multiple possible inversions- I'll also throw in Critic-Proof (a work is popular despite getting panned by critics), Critical Dissonance (a work is held in high regard in spite of critics panning it, or praised by critics and pelted with rotten vegetables by the general public), and Acclaimed Flop (a work is highly praised and possibly even showered with awards... and makes $5 and some pocket lint at the box office.)
Edited by Scorpion451
What is the opposite trope of Hype Backlash? Can someone tell me?