head to head
Call of Duty: Modern Warfare asks more than Half-Life 2, and the gap is reads.

Execution · Pure Mechanics
A tactical military shooter where aim against human opponents is the deciding factor.

Execution · Pure Mechanics
Landmark FPS built on physics puzzles and tight gunplay.
Call of Duty: Modern Warfare leans Execution (Pure Mechanics); Half-Life 2 leans Execution (Pure Mechanics).
Call of Duty: Modern Warfare leans clearly harder on execution.
Call of Duty: Modern Warfare
aim and reflexes decide engagements
Half-Life 2
Gravity gun and shooting demand precision.
Call of Duty: Modern Warfare leans clearly harder on reads.
Call of Duty: Modern Warfare
predicting human opponents' positioning
Half-Life 2
Combine AI scripted, non-adaptive.
Call of Duty: Modern Warfare leans a little harder on variance, though the gap is small.
Call of Duty: Modern Warfare
spawns and loadout drops vary
Half-Life 2
Almost no randomness.
Call of Duty: Modern Warfare leans a little harder on optimization, though the gap is small.
Call of Duty: Modern Warfare
loadouts and map knowledge solvable
Half-Life 2
Linear progression with no builds.
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.