I always said that I would never try Master difficulty due to the artificial difficulty but I decided, why not I'll try it out. These are my thoughts and impressions over the 10 hours that I've played of it.
Enemy mages are horrible to fight against due to the double damage from magic. It's basically a permanent Apprentice stone without the magic buff.
Spiders are actually tough to fight due to poison doing double damage.
My 1st encounter outside of Helgan was the camp with 3 bandits and I had to use Battle cry on them. On Adept I'd just run right in and slug it out but I had to use Battlecry and then take out the bandits one at a time.
I find that Smithing is essential on Master or else you'll be gouging yourself in the eye. Right now I had a Steel Plate armor equipped with Steel Boots, Steel Helmet and Iron 25% One Handed Gauntlets equipped. I'm right around 320 Armor Rating which is way higher then I normally would be. Basically by doing what I'm doing, I'm trying to overcome the 50% less damage X2 more damage.
I fought a couple of Dragon's but they were just regular Dragons, once I get to fight an Elder I can access more but Dragons are still the same as normal just shield bash when they breath and back kite when they chomp.
There's a lot of encounters that I normally would have fought but I've had to run away from. I almost died from an Ice wolf, heck I almost died from a Mudcrab, now that would have been embarrassing.
So far I'm loving Master although I don't know if I would ever play as a Mage or a Two Handed character on Master difficulty. I doubt I'll ever go up to Legendary, the only change would be me focusing on Smithing and getting that up to 100 and forging myself a Daedric Armor Set and Daedric Sword. I'm gonna go back and do more, I do dread going to Solsteim and also doing the Dawnguard questline.