Building comparison
head to head
Fallout 3vsPortal 2
Neither is simply harder - they are hard in different places. Fallout 3 demands more variance; Portal 2 demands more optimization.
Fallout 3
Optimization · Pure Optimization
A VATS-heavy wasteland RPG won by perk and build optimization.
Portal 2
Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Fallout 3 leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Fallout 3Portal 2
Axis by axis
Execution3 vs 3
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Fallout 3
VATS-leaning combat, low aim demand
Portal 2
Portal placement requires some precision but timing is lenient.
Reads1 vs 0
Fallout 3 leans a little harder on reads, though the gap is small.
Fallout 3
Scripted enemies
Portal 2
No opponent; puzzles are static.
Variance2 vs 0
Fallout 3 leans clearly harder on variance.
Fallout 3
Loot rolls, SPECIAL checks
Portal 2
Puzzles are deterministic with no randomness.
Optimization7 vs 9
Portal 2 leans clearly harder on optimization.
Fallout 3
Perk and build planning carries the run
Portal 2
Solving the puzzle's logic IS the entire game.
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.