Outside of dragons there's about 4-6 spots in the game that are difficult on NM even if you know what you're doing: Pride demon at the start (unless you cheese it), Envy demon, In Your Heart's last checkpoint, Crestwood's story rift with 4 waves, and Rage demons mixed with Terrors, the ending checkpoint, and boss in Here Lies the Abyss, and if you tackle a couple areas earlier than expected, anything with Spiders, or archers and lieutenants/bosses (end of Fallow Mire).
The issue is, most of those can be outleveled, out-geared etc.
That said, Origins was pretty easy too with a good setup.
Envy's far harder than Alexius, whose only trick is to spawn a couple rifts in the middle of battle. Alexius can be stucklocked, or knocked down with Shatter Shot/Charging Bull/Whatever, and he's only really got two things you have to watch out for (Glyphs being the big one).