I play in Expert. I do not mind for Master because it starts to bother me. It's not challenging, it's just annoying.
But I must tell you: Giants are a bit more complicated to defeat than Dragons. Seriously.
But I must admit: A Fire dragon kicks my ass. I am lvl 22 and, well, a nord with 50% + 40% frost resistance. Frost Dragons does nothing to me. I am a stealth based-light armor player. I just melee 'em!
Fire dragons are a censored problem... altough easy if you got the skills.
Dragons should really be more difficult. a bit more HP would be enough.