I think for a game like horizon the quests need to be as interesting and as varried as the story. If they dont break up the combat with other tasks they need to add more grander and creative combat scenarios, I did enjoy attacking and defending large outposts with a crazy variety of big and small robos, they need more of that.
I just remembered that there was other types of quests in zero dawn, at the very beginning where little Aloy gets lost and explores the old world and later during the proving where you do that race, there needs to be more of those sort of quests to break the monotony of killing 1000s of robos and tribesmen.
I found the ps3 uncharted games suffered from this, where you would just kill,kill,kill for what seemed long periods of time. UC4 got the balance far better and would break up the combat with other sections.
However this is pretty subjective, I understand some gamers prefer to just kill.
Its also pretty depended on the type of game.