head to head
Neither is simply harder - they are hard in different places. Grand Theft Auto V demands more reads; No One Lives Forever 2: A Spy in H.A.R.M.'s Way demands more optimization.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.

Execution · Practiced Mastery
Stylish 60s spy FPS mixing stealth routes, gadgets, and gunfights.
Grand Theft Auto V leans Execution (Practiced Mastery); No One Lives Forever 2: A Spy in H.A.R.M.'s Way leans Execution (Practiced Mastery).
No One Lives Forever 2: A Spy in H.A.R.M.'s Way leans a little harder on execution, though the gap is small.
Grand Theft Auto V
Driving and shooting demand decent inputs.
No One Lives Forever 2: A Spy in H.A.R.M.'s Way
Gunplay and stealth timing through guarded levels
Grand Theft Auto V leans clearly harder on reads.
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
No One Lives Forever 2: A Spy in H.A.R.M.'s Way
Guards run scripted patrols and alert states
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Grand Theft Auto V
Some mission and lobby randomness.
No One Lives Forever 2: A Spy in H.A.R.M.'s Way
First-run patrol uncertainty, then learnable
No One Lives Forever 2: A Spy in H.A.R.M.'s Way leans clearly harder on optimization.
Grand Theft Auto V
Heists, money loops, builds learnable.
No One Lives Forever 2: A Spy in H.A.R.M.'s Way
Gadget use, stealth routing, and skill upgrades
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.