head to head
Garry's Mod asks more than Firewatch, and the gap is reads.

Optimization · Light / Casual
A first-person mystery about a fire lookout in a Wyoming forest.

Reads · Light / Casual
Source-engine sandbox whose community modes range from building to social deduction.
Firewatch leans Optimization (Light / Casual); Garry's Mod leans Reads (Light / Casual).
Garry's Mod leans a little harder on execution, though the gap is small.
Firewatch
Walking and radio dialogue only.
Garry's Mod
Varies by mode; base sandbox is undemanding
Garry's Mod leans clearly harder on reads.
Firewatch
No adaptive opposition.
Garry's Mod
Social deduction modes like TTT involve humans
Garry's Mod leans clearly harder on variance.
Firewatch
Minor environmental discoveries.
Garry's Mod
Hidden roles and player chaos in popular modes
Garry's Mod leans a little harder on optimization, though the gap is small.
Firewatch
Few systems to optimize.
Garry's Mod
Contraption building rewards systems knowledge
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.