Ignore the bad reviews. They're by people who have no idea what film actually looks like. Some movies are naturally grainier than others, and this Blu-ray does a beautiful job at representing Bullitt in its purest form outside of a cinema.
No, Bullitt won't melt your eyeballs in HD, but then again not every movie will look like Transformers. Until people realise this, we'll keep getting ignorant reviews like those above.