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
A heavyweight sci-fi FPS pitting ISA soldiers against the Helghast with famously weighty gunfeel.

Execution · Pure Mechanics
Console shooter execution across scripted set pieces and once-massive human multiplayer.
Killzone 2 leans Execution (Pure Mechanics); Resistance 2 leans Execution (Pure Mechanics).
Killzone 2 leans a little harder on execution, though the gap is small.
Killzone 2
Weighty gunplay punishes imprecise aim hard
Resistance 2
Weapon handling and boss dodging demand console-shooter precision
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Killzone 2
Multiplayer opponents adapt; campaign AI doesn't
Resistance 2
60-player multiplayer rewarded reading humans; campaign Chimera don't adapt
Killzone 2 leans a little harder on variance, though the gap is small.
Killzone 2
Modest spawn and objective rotation noise
Resistance 2
Campaign encounters are set pieces
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Killzone 2
Class unlocks and map control are learnable
Resistance 2
Exotic weapon choice and class co-op roles add planning
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.