Just killed Alexius on nightmare with two potions left after like 10 tries. Then the game bugs out during the cutscene, back to the start of the fight it is.... GRRRRRRRRRRRRR....
Atleast I know I can do it.
PC controls haven't been so bad for me, except for the fact that you can't zoom out enough when in tactical mode. You can't order your character to close / disrupt rifts because they're outside the view that way. Also, when you do order them to do such a thing during tactical, the commands tend to fail.
Another common bug I have is that the War Room menus become unclickable. This is solved by pressing the windows key repeatedly for me (using borderderless windowed mode).
Companion AI is a mess when you're trying to get them to hold their ground. The command to hold position should stick even after using stuff like Shield Wall on a character.