Every now and then, a movie comes along that’s so good it ruins a genre forever, because it sets a benchmark that can’t be beaten. When the credits started rolling on one of them, Quentin Tarantino was hit with the sobering realisation that one of his favourite forms of cinema had been ruined forever. It doesn’t happen often, but there are more than a few titles that become known as perennial party-poopers. Steven Spielberg has done it twice, be…