Indeed, bad CG can ruin an otherwise great movie. My go-to example is the high-concept 2008 Mexican Sci-fi thriller Sleep Dealer - had the director simply chose

Indeed, bad CG can ruin an otherwise great movie. My go-to example is the high-concept 2008 Mexican Sci-fi thriller Sleep Dealer - had the director simply chosen to have the biggest action setpieces happen off-screen or be otherwise implied, it might have been enough of a success to make back its modest 2.5M investment, but the abysmal CG they were able to get on that budget brought the whole film down.