The campaigns are high quality and the Gamestar review didn’t deny that.
But they didn’t like the choice of presentation. That is entirely a taste thing and that’s why it likely didn’t affect the score as much.
AoE2 told the story from the perspective of a person for the Middle Ages while AoE4 has a outside narrator.
Even in the missions you don’t hear the characters talk, only the modern day narrator.
This is less immersive and makes you feel like you play a documentary.
It’s up to personal taste if you like that or not. Maybe someone thought the old voice lines were cringe and is happy about the new presentation or the other way round a different person feels pulled out of the experience if they hear the narrator talks about the side mission they just completed.