Brewers use hops, a small bitter flowering plant, to provide a counterbalancing aroma and taste to beer. The basic idea is not unlike what you would find in a good wine. As you drink, the malty beer washes over your tongue, bringing you body and sweetness. As you swallow, the hops hit the bitter taste buds in the back of your mouth, serving as a tonic, leaving (hopefully) a refreshing taste.
You hate beer — if you do hate beer — because most of the beers you've tried are unbalanced. All you can taste is hops. And with nothing to balance them, hops taste nasty.