I just started my Inferno run through with my lvl 60 Barbarian. Honestly, I thought the game was pretty easy on Nightmare. I beat Diablo without dying. I maybe died 8 times on the whole play through on nightmare. There was one part when I ran into some crazy enemies who threw huge bombs, and they were illusionist desecrators. I was constantly running because if I stopped I would get bombarded by like 10 bombs and I would get desecrated anywhere i stood for more than a few seconds. I died twice before I was able to get past them. Thats really the hardest part Ive come across so far.