head to head
Neither is simply harder - they are hard in different places. Fallout: New Vegas demands more execution; Return of the Obra Dinn demands more optimization.

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

Optimization · Pure Optimization
A pure deduction puzzle with a single solvable answer set.
Fallout: New Vegas leans Optimization (Pure Optimization); Return of the Obra Dinn leans Optimization (Pure Optimization).
Fallout: New Vegas leans clearly harder on execution.
Fallout: New Vegas
Shooter inputs with VATS assist
Return of the Obra Dinn
No mechanical execution required
Fallout: New Vegas leans a little harder on reads, though the gap is small.
Fallout: New Vegas
Scripted factions and enemies
Return of the Obra Dinn
Static scenes, no opponent
Fallout: New Vegas leans clearly harder on variance.
Fallout: New Vegas
Some loot and crit RNG
Return of the Obra Dinn
Fully deterministic puzzle
Return of the Obra Dinn leans clearly harder on optimization.
Fallout: New Vegas
Faction routing, perks, builds heavily rewarded
Return of the Obra Dinn
Pure deductive logic on a fixed manifest
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.