head to head
Metal Gear Solid 4: Guns of the Patriots asks more than Zombie Army Trilogy, and the gap is optimization.

Optimization · Practiced Mastery
Series finale blending stealth with active battlefields and heavy cinematics.

Execution · Practiced Mastery
A co-op horde shooter testing sniper aim and chokepoint planning against scripted waves.
Metal Gear Solid 4: Guns of the Patriots leans Optimization (Practiced Mastery); Zombie Army Trilogy leans Execution (Practiced Mastery).
Zombie Army Trilogy leans a little harder on execution, though the gap is small.
Metal Gear Solid 4: Guns of the Patriots
flexible gunplay alongside sneaking
Zombie Army Trilogy
Long-range sniping and horde kiting demand steady aim
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Gear Solid 4: Guns of the Patriots
battlefield factions act on scripts
Zombie Army Trilogy
Undead waves follow predictable spawn scripts
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Gear Solid 4: Guns of the Patriots
mid-battle chaos mostly cosmetic
Zombie Army Trilogy
Spawn timing varies a little between runs
Metal Gear Solid 4: Guns of the Patriots leans clearly harder on optimization.
Metal Gear Solid 4: Guns of the Patriots
camo, gear, and route knowledge per act
Zombie Army Trilogy
Choke points, trap placement and ammo economy reward 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.