head to head
Neither is meaningfully harder - they pose close to the same test. The widest gap is reads, and it is a single point.

Execution · Practiced Mastery
The sequel adding Horde mode to the campaign-plus-versus cover shooter formula.

Execution · Practiced Mastery
The console FPS landmark that introduced Master Chief and the ring world.
Gears of War 2 leans Execution (Practiced Mastery); Halo: Combat Evolved leans Execution (Practiced Mastery).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War 2
Gnasher battles and movement tech set the ceiling
Halo: Combat Evolved
Aim, grenade timing, and vehicle control
Gears of War 2 leans a little harder on reads, though the gap is small.
Gears of War 2
Human opponents in versus drive prediction play
Halo: Combat Evolved
Multiplayer duels reward reading humans
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War 2
Horde spawns add mild randomness
Halo: Combat Evolved
Covenant AI varies tactics slightly
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Gears of War 2
Power-weapon timing and positioning are solvable
Halo: Combat Evolved
Weapon sandbox knowledge and encounter routing
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.