Ezreal is a very mid game oriented ADC, he's also weird in that he's burst instead of sustained damage, similar to say Graves. He's strong if you know how to play him well, but he takes some know-how. He's weak early and lackluster late.
The reason he feels weak to you most likely is because over 50% of games have either Jinx or Vayne involved, and he gets outclassed heavily by the two of them due to sheer damage output. A lot of Ezreal's damage comes from weaving abilities and auto attacks together to get the most out of his spellblade, whichever he happened to choose. I prefer Manamura/Triforce in most situations, but there's merit to blue build, for bot lane if you want to do that instead.