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
A cartoonish horde shooter sequel of planet-hopping monster massacres.

Execution · Practiced Mastery
A campy 16-bit run-and-gun about rescuing neighbors from B-movie monsters.
Serious Sam 2 leans Execution (Practiced Mastery); Zombies Ate My Neighbors 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.
Serious Sam 2
Sustained horde-clearing aim and strafing
Zombies Ate My Neighbors
Dodging monsters while sniping with squirt guns
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Serious Sam 2
Enemy waves are entirely scripted
Zombies Ate My Neighbors
Monster movie AI is fully patterned
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Serious Sam 2
Cartoon set-pieces surprise once
Zombies Ate My Neighbors
Victim placement varies slightly per level
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Serious Sam 2
Target priority and arena routes are learnable
Zombies Ate My Neighbors
Weapon-versus-monster matchups and level routing
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.