head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; Neverwinter Nights 2 demands more variance.

Optimization · Pure Optimization
A faction-driven RPG-shooter where build and route planning shape every ending.

Optimization · Pure Optimization
A deep 3.5E optimization puzzle where prestige class chaining and feat synergies determine party effectiveness.
Fallout: New Vegas leans Optimization (Pure Optimization); Neverwinter Nights 2 leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Neverwinter Nights 2
Tactical pause negates twitch; positioning is deliberate not reactive
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout: New Vegas
Scripted factions and enemies
Neverwinter Nights 2
Companion AI and enemy scripting are fixed, non-adaptive routines
Neverwinter Nights 2 leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Neverwinter Nights 2
Hidden enemy stat blocks and variable dungeon RNG create unknowns
Neverwinter Nights 2 leans a little harder on optimization, though the gap is small.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Neverwinter Nights 2
3.5E feat synergies and prestige class planning define optimal builds
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.