I would give returnal a low score because I found the game too repetitive.
Scores can’t ever be objective.
I agree they should try hard, as it is their job. But a score will be always quite subjective and/or influenced by others.
Welcome to the roguelike genre. They are meant to be that way. Also, if you want to talk about this so called "repetitive" feeling, you do realize every game is repetitive in its own way yes? In Dark Souls, you start off, explore, kill boss/enemies, new area, rinse and repeat.
In FPS games you, walk into a room, shoot demons/monsters/bad guys/, walk into the next room, rinse and repeat.
In Uncharted you do the same thing, go into an area, jump into cover, shoot bad guy, go to next area and rinse and repeat.
Every game in existence is repetitive in its own way. You are confusing "I felt it was repetitive" with "bad gameplay loop" Returnal is not a game for everyone because roguelikes are niche. But the way it does its gameplay loop is very well done imo. There is nothing wrong with not liking Returnal, it's just a game that is not for you. If you did write a review, then it will be your responsibility to state at the very beginning that you are not a fan of roguelikes to begin with. This way, you are transparent, do not look like an idiot and most importantly, honest.
You find other games more enjoyable because you find their "repetition/gameplay loop" more suited towards your liking and that's fine.
And yes, scores can be subjective if you know how to do your job right. I've been reviewing games for over 10 years. They 100% can be objective with a mix of subjection.