I just had my first dragon fight (being level 5). Well, not exactly my fight, had 5 more npcs with me. All I can say is, dragon fights in skyrim is a total experience on its own. You got to see it to believe it.
Anyways, being a melee fighter, I had to wait until the npc archers forced the dragon to land. Still, I could not get near it, as it seemed he preferred to target me when I was getting close. Luckily, I was able to get a bow and arrows from a corpse nearby - dragon attacked a guard post outside the city and killed all but one guard. Lowered his health by shooting arrows, hiding between ruined post to avoid fires, and then a final running blow from my 2-hand war hammer. It was epic.
I hope, though, that on higher levels I will be able to bring one down on my own, even as a melee fighter. Right now, it seems just impossible.