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 free co-op top-down shooter about a marine squad purging alien-infested colonies.

Execution · Practiced Mastery
Claustrophobic post-apocalyptic shooter where bullets double as currency.
Alien Swarm leans Execution (Practiced Mastery); Metro 2033 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.
Alien Swarm
Top-down aim and friendly-fire discipline
Metro 2033
scarce-ammo gunfights punish sloppy aim
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Alien Swarm
Swarm AI scripted by director triggers
Metro 2033
mutants and bandits follow scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Alien Swarm
Spawn timing varies modestly
Metro 2033
hidden moral points and supplies first run
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Alien Swarm
Class loadouts and route knowledge decide runs
Metro 2033
ammo-as-currency economy and stealth 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.