head to head
Tony Hawk's Project 8 asks more than Half-Life 2, and the gap is execution.

Execution · Pure Mechanics
Landmark FPS built on physics puzzles and tight gunplay.

Execution · Pure Mechanics
Trick-execution mastery and optimised line routing for combo scores.
Half-Life 2 leans Execution (Pure Mechanics); Tony Hawk's Project 8 leans Execution (Pure Mechanics).
Tony Hawk's Project 8 leans clearly harder on execution.
Half-Life 2
Gravity gun and shooting demand precision.
Tony Hawk's Project 8
Combo stringing, balance meters and Nail-the-Trick demand trained hands
Half-Life 2 leans a little harder on reads, though the gap is small.
Half-Life 2
Combine AI scripted, non-adaptive.
Tony Hawk's Project 8
Solo score runs against static environments
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.
Tony Hawk's Project 8
Levels are fully deterministic
Tony Hawk's Project 8 leans clearly harder on optimization.
Half-Life 2
Linear progression with no builds.
Tony Hawk's Project 8
Line routing for maximum combo score rewards study
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.