head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is variance, and it is a single point.

Optimization · Practiced Mastery
Co-op first-person zombie RPG about improvised weapons on a resort island.

Optimization · Practiced Mastery
A tense survival horror where one bite kills your survivor for good.
Dead Island leans Optimization (Practiced Mastery); ZombiU leans Optimization (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Dead Island
first-person melee timing and stamina
ZombiU
Deliberate cricket-bat timing and panic inventory management
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Dead Island
zombies are scripted swarms
ZombiU
Zombies shamble on fixed logic
ZombiU leans a little harder on variance, though the gap is small.
Dead Island
weapon drops and spawns add noise
ZombiU
Permadeath runs face unknown spawn placements
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Dead Island
weapon mods and skill builds carry late game
ZombiU
Route knowledge, supply caching, safehouse planning
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.