Jaws
This movie introduced me to horror when I was less than ten years old and every time I rewatch it I keep thinking it’s an excellent film. The way in the first half of the movie they don't show you the shark increases the degree of fear you can feel because the imagination is more powerful than any image. Even knowing perfectly well what a shark looks like I imagined something even worse. More evil. A perverse man-eating being. The music is also iconic and very effective in generating tension and achieving what I'm describing.
The only thing I disliked is that the last half of the movie drops the tension for more of an adventure story. The shark is already shown and the effect is completely gone. It's well done, but I find the first half to be superior.
I hate that most of the bad reviews are not because of the quality of the product, but because of how it portrays sharks. It's fiction. It achieved its goal. Get over it.