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

Execution · Pure Mechanics
Open-world racing testing car control and line discipline with light tuning underneath.

Execution · Pure Mechanics
Landmark FPS built on physics puzzles and tight gunplay.
Forza Horizon 2 leans Execution (Pure Mechanics); Half-Life 2 leans Execution (Pure Mechanics).
Forza Horizon 2 leans a little harder on execution, though the gap is small.
Forza Horizon 2
Racing lines, braking points and car control lead everything
Half-Life 2
Gravity gun and shooting demand precision.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Forza Horizon 2
Drivatar AI mimics styles but stays effectively scripted
Half-Life 2
Combine AI scripted, non-adaptive.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Forza Horizon 2
Weather shifts grip slightly; courses are fully known
Half-Life 2
Almost no randomness.
Forza Horizon 2 leans a little harder on optimization, though the gap is small.
Forza Horizon 2
Car tuning and route knowledge reward preparation
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.