head to head
Portal 2 asks more than Fable III, and the gap is optimization.

Optimization · Pure Optimization
An action RPG that crowns you king and tests your treasury more than your sword.

Optimization · Pure Optimization
A first-person puzzle game where seeing the solution is the whole skill.
Fable III leans Optimization (Pure Optimization); Portal 2 leans Optimization (Pure Optimization).
Same score on execution - which means the number cannot separate them. The difference is in what each one asks of you.
Fable III
Simplified combat rarely punishes
Portal 2
Portal placement requires some precision but timing is lenient.
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Fable III
Scripted enemies
Portal 2
No opponent; puzzles are static.
Fable III leans a little harder on variance, though the gap is small.
Fable III
Largely fixed world
Portal 2
Puzzles are deterministic with no randomness.
Portal 2 leans clearly harder on optimization.
Fable III
Treasury management and kingdom promises drive the endgame
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.