The Bigger Mistake
I can deal with bad acting in a horror film. The two leads (Keiko Kirishima as Detective Hitomi and Ryuhei Matsuda as dream guy Kyoichi) were uniformly terrible, but I eventually accepted their stilted lack of affect as an aspect of the film's style - an unfortunate aspect, perhaps, but not a wholly fatal flaw. And everything/everyone else was good enough get me through the rough spots.
As a genre fan, I had a bigger problem with THE GUY. Director Shinya Tsukamoto did a wonderful job as the human version of the villain character, but his effects team created these STUNNING, Thing-quality props & makeups for The Guy's nightmare-monster incarnations -- and he barely let us see them! A shaky, blurry, three-frame glimpse here and there, but that's it. I felt cheated I tell you, robbed! Especially upon watching Tsukamoto's production documentary and seeing just how goddam great (and inventive and terrifying and lovingly detailed) the creature effects really were.
The bucher-headed thing that chases Masanobu Ando's Detective Wakamiya down the street is AMAZING. The flayed and staring monstrosity that threatens Hitomi and Kyoichi in the climactic battle is even better. Can't understand why a director would order the creation of such splendid work and then let it go so utterly to waste. A goddam shame is what it is...
You must have been so afraid, Cassie... Then you saw a cop.