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 loud, high-endurance test of accurate crowd control against relentless scripted enemy swarms in open arenas.

Execution · Pure Mechanics
Tests perceptual speed and motor execution under accelerating piece gravity.
Serious Sam: The First Encounter leans Execution (Pure Mechanics); Tetris DX leans Execution (Pure Mechanics).
Tetris DX leans a little harder on execution, though the gap is small.
Serious Sam: The First Encounter
Sustained accurate fire against enormous enemy hordes demands constant aim
Tetris DX
Precise placement under accelerating gravity decides every game
Same score on reads - which means the number cannot separate them. The difference is in what each one asks of you.
Serious Sam: The First Encounter
All enemies are scripted and follow fixed rush patterns
Tetris DX
Solo stacking with no opponent to model
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Serious Sam: The First Encounter
Enemy placement is consistent across runs; no hidden information
Tetris DX
Random pieces are bounded and rapidly mappable
Same score on optimization - which means the number cannot separate them. The difference is in what each one asks of you.
Serious Sam: The First Encounter
Enemy priority and positioning strategy are learnable but shallow
Tetris DX
Stacking patterns and scoring strategy are well solved
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.