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 · Practiced Mastery
An arcade FPS that scores you for killing enemies in the most creative ways possible.

Optimization · Practiced Mastery
Threading precise inputs through scripted guard gauntlets aboard a controlled and memorisable facility.
Bulletstorm leans Execution (Practiced Mastery); Metal Gear Solid 2: Sons of Liberty leans Optimization (Practiced Mastery).
Bulletstorm leans a little harder on execution, though the gap is small.
Bulletstorm
Leash, kick, and shot timing drive skillshot chains
Metal Gear Solid 2: Sons of Liberty
First-person aim and guard reaction windows demand precise input
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Bulletstorm
Enemies are scripted fodder for your combos
Metal Gear Solid 2: Sons of Liberty
Guards radio for backup on scripted triggers, not adaptive tactics
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Bulletstorm
Arenas and spawns are fixed and learnable
Metal Gear Solid 2: Sons of Liberty
Alert timers and item pickups create some hidden-state tension
Metal Gear Solid 2: Sons of Liberty leans a little harder on optimization, though the gap is small.
Bulletstorm
Maximising skillshot score per arena is a solvable puzzle
Metal Gear Solid 2: Sons of Liberty
Chokepoint memorisation and radar manipulation are learnable and repeatable
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.