Ok I am really thinking the difficulty spread is pretty imbalanced for the solo game here.
After whizzing through Expert for a chunk of Act 1 with a fresh Wizard, I curiously slid up to Master(a difficulty LOCKED until finishing the campaign once, or importing an old character that has finished the PS3 version will open it up early as I did), and since the majority of new players won't have access to this difficulty I was pretty bummed at how negligible the scale difference in challenge has been.
Enemies have an insane amount of health on Master, which protracts each fight longer than most probably care to deal with, but sadly they lack the offensive bite to balance this change. I am geared up in orange legendaries thanks to the mailbox system(curious why I am gifted legendaries by PSN friends? I have YET to die or see the Nemesis system even on this difficulty!) It feels like me and the enemy mobs are just hitting each other with whiffle bats on Master. I do weak damage geared up, and they barely scratch me either. Eventually I will win the attrition war and I have.
Basically, game is way too easy, possibly too easy for solo players(at least through the bulk of Act 1 solo with a new char). Co-op however has proven different as the stat bump from playing online has shown the monsters get pretty dangerous, but this is really just stressing the solo mode. PS3 version was no joke above Hard playing solo, PS4 version is kind of a joke so far.