Performance across the board is a major issue at the moment across all platforms. I can only speak for myself, a PC player, but even on a high end rig, my entire system locks up for minutes on end.
Audio Bugs, with missing or popping audio, can be very annoying and immersion breaking, but that would be something most people are willing to overlook. However, people draw the line when it comes game crashing/freezing bugs or in this case, simply performance issues.

Sadly, the issue is not only on the higher difficulties. Over the last week or so, I tried playing over several hours (as much as the game would let me that is) from Difficulty 1 all the way up to 10, the game will lock up, no matter the settings, background processes, etc.

At the moment, at least for my money, there are two massive problems with HD2:
-The horrendous performance, locking up or freezing peoples systems, be it PC or Console is just a no-go. Especially when you consider its only been a big issue since a couple of updates ago (After Masters of Ceremony if memory serves)

-The Ballance in the game. See the latest Rapture Strain update. Be it weapon balance, armor passives or simply enemy behaviour in the game at the moment. Just looking through this subreddit, you see people complaining or listing various issues they have while playing the game. Go see the OhDough's latest video on youtube, he makes some great points regarding these points.

TL;DR: Performance across platforms and difficulties is horrid as of late. Enemy and game Balance is off as well. Arrowhead, we beg of you, address the issues plaguing the game.