This expression captures something that's unexpectedly impressive or can't be underestimated. 'Dark horse' might come close, but it's more about hidden potential in competitions. 'Sleeper hit' works for media that exceeds expectations, like how 'Parasite' was initially overlooked before sweeping awards.
'Underdog' carries some overlap, though it emphasizes overcoming disadvantages rather than surprise competence. In gaming circles, 'hidden gem' describes underappreciated masterpieces like 'Stardew Valley' before its popularity exploded. The nuance changes based on context - there's no perfect 1:1 translation, only approximations for different situations.