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

Execution · Pure Mechanics
A run-and-gun arcade shooter that is almost pure twitch execution.

Execution · Pure Mechanics
A loud, high-endurance test of accurate crowd control against relentless scripted enemy swarms in open arenas.
Metal Slug 5 leans Execution (Pure Mechanics); Serious Sam: The First Encounter leans Execution (Pure Mechanics).
Metal Slug 5 leans a little harder on execution, though the gap is small.
Metal Slug 5
precise dodge/shoot run-and-gun demands
Serious Sam: The First Encounter
Sustained accurate fire against enormous enemy hordes demands constant aim
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug 5
enemy waves are fully scripted patterns
Serious Sam: The First Encounter
All enemies are scripted and follow fixed rush patterns
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Metal Slug 5
minor drop and spawn randomness
Serious Sam: The First Encounter
Enemy placement is consistent across runs; no hidden information
Serious Sam: The First Encounter leans a little harder on optimization, though the gap is small.
Metal Slug 5
weapon pickup and route memorization
Serious Sam: The First Encounter
Enemy priority and positioning strategy are learnable but shallow
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.