head to head
Neither is harder. They score identically on all four axes, so the difference between them is in kind, not degree.

Execution · Practiced Mastery
Gothic PS1 action horror of brutal melee against Victorian monsters.

Execution · Practiced Mastery
A cartoonish horde shooter sequel of planet-hopping monster massacres.
Nightmare Creatures leans Execution (Practiced Mastery); Serious Sam 2 leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Nightmare Creatures
Combo timing and dodges against tough monsters
Serious Sam 2
Sustained horde-clearing aim and strafing
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Nightmare Creatures
Creatures use fixed attack patterns
Serious Sam 2
Enemy waves are entirely scripted
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Nightmare Creatures
Ambush placement unknown first time through
Serious Sam 2
Cartoon set-pieces surprise once
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Nightmare Creatures
Adrenaline meter management and route learning
Serious Sam 2
Target priority and arena routes are learnable
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.