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

Execution · Pure Mechanics
A rally racer where mastering precise car control against tricky terrain is everything.

Execution · Pure Mechanics
A loud, high-endurance test of accurate crowd control against relentless scripted enemy swarms in open arenas.
Colin McRae: Dirt 2 leans Execution (Pure Mechanics); Serious Sam: The First Encounter leans Execution (Pure Mechanics).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Colin McRae: Dirt 2
precise rally driving and braking required
Serious Sam: The First Encounter
Sustained accurate fire against enormous enemy hordes demands constant aim
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Colin McRae: Dirt 2
no adaptive opponents, mostly time trials
Serious Sam: The First Encounter
All enemies are scripted and follow fixed rush patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Colin McRae: Dirt 2
weather and surface conditions vary
Serious Sam: The First Encounter
Enemy placement is consistent across runs; no hidden information
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Colin McRae: Dirt 2
car tuning and racing lines solvable
Serious Sam: The First Encounter
Enemy priority and positioning strategy are learnable but shallow
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.