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
Landmark FPS built on physics puzzles and tight gunplay.

Execution · Pure Mechanics
A classic beat-em-up demanding execution against scripted enemy waves.
Half-Life 2 leans Execution (Pure Mechanics); Teenage Mutant Ninja Turtles III: The Manhattan Project leans Execution (Pure Mechanics).
Teenage Mutant Ninja Turtles III: The Manhattan Project leans a little harder on execution, though the gap is small.
Half-Life 2
Gravity gun and shooting demand precision.
Teenage Mutant Ninja Turtles III: The Manhattan Project
beat-em-up timing and enemy juggling
Half-Life 2 leans a little harder on reads, though the gap is small.
Half-Life 2
Combine AI scripted, non-adaptive.
Teenage Mutant Ninja Turtles III: The Manhattan Project
enemies run simple fixed scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Half-Life 2
Almost no randomness.
Teenage Mutant Ninja Turtles III: The Manhattan Project
minor enemy spawn randomness
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Half-Life 2
Linear progression with no builds.
Teenage Mutant Ninja Turtles III: The Manhattan Project
character choice and route memorization
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.