He's effectively a mixed damage ranged assassin who is extremely safe, gets his items quickly and never has a "weak" stage in the game.
Honestly I'd say he's one of the best burst champions in the game right now, which just isn't right since the only item that he gets now for burst damage is Luden's. I keep seeing Ezreals 2-shot people (or 1 shot if you classify W->Q as a oneshot), and honestly, it just doesn't feel right at all.
Essentially what I'm trying to say is that Ezreal being this ranged assassin/burst mage does not make sense with his overall design and in terms of gameplay it just isn't right for such a safe champion to possess all of this burst damage without committing to a full AP build.
Everyone is talking about getting oneshot by assassins and yet no one is complaining about Ez xD