The default difficulty is [censored] easy, how is master (hardest) difficulty? Is it like mind-numbingly difficult, and can you face enemies head-on or do you have to kite and force yourself to be a mage or archer?

Its hard, but not bad like Oblivion's 'give them 45763485602345762346 hitpoints' hard.

Enemies take about 10 more hits and kill you in two hits.
Fake difficulty at its finest.
Dont try to fight dragons, because their breath will kill you in two seconds (and its undodgeable, as you may know)

i didnt get that impression at all. moreover, i feel like the harder difficulty kind of exposes the fake rpg mechanics of the game. this is basically a fallout without guns. but its done well enough so that on easy mode youre swimming through enemies and levels without noticing it.

Pretty sure stealthy illusion+conjuration build is best again for max difficulty.

I haven't played on Normal for comparison...started on Master and have stayed there throughout (20 hours in so far). It's not easy, but not really that hard either...granted, I'm also coming off of just finishing Dark Souls, so that may be coloring my opinion somewhat. Some playstyles that are probably perfectly valid for Normal (destruction mage, most obviously) don't really work for Master. But now that I'm an archer, I'm doing fine. Smithing/enchanting/alchemy seem to be sorta non-optional, as do armor skill perks.

Oh, also the Become Ethereal shout is a serious lifesaver for Master difficulty, especially against mages (who otherwise go right through my armor if they get close).