Except it's not, how can anyone honestly believe this? Please tell me what exactly is "objective good game design."
Have you ever designed a videogame ?
Well, it's like building an house.
A game designer (with complete knowledge about level design, gameplay mechanics, etc) can easily say if a game is well built or not.
Yes, there are some choices that can make the difference in a bad or good way, but in the end it's very important have a solid "structure" of the game.
A simple example:
Some platforms and Mario.
The goal of the level designer is to create a challenging part for the final stage and he/she chooses to place the last three platforms at the same level at an "half-jump" distance between them.
This is a bad choice because the final stage is not challenging at all.
He/She change his/her mind and sets up three platforms at full-jump distance with a death zone under them. If Mario falls he dies.
This choice is more challenging but since the player has only three lives, this part may get some players frustrated.
The (last) idea is to place two platforms at 3/4-jump distance and the last one at full-jump distance, but with an enemy over the last platform and no death zone if Mario falls. This choice is more challenging than the first one, there is some engaging jumping to do and a "risk" on the last platform. Most of the players may manage to do the first two jumps with little effort, stand over the second platform until the enemy is far on the third platform and face the last jump. If the Mario doesn't make a good jump he will not die and the player may quickly retry again from the first of the three platforms.
I think you can easily spend some words on each of the three problems and maybe say which of them is objectively a good design.
I hope I made my point
(If not there are a lot of other examples, maybe even straighter!)
Ps I don't want to teach nothing to anyone, mine are just an example !
