I think it depends on the game
if the game in question is particularly rewarding in its many game impacting choices or its mechanics when you play it, then I think first hand experience is essential
story driven games like undertale can be mostly experienced in a playthrough. but you will be noticeable robbed by some of the smaller spoiler moments like in papyrus's fight when you hold up during the last attack:
your blue heart keeps going up and the ceiling of the box actually raises to accommodate you. I give full credit to that cool moment being satisfying because the player in this moment will be holding the up button the entire time, this interaction is less satisfying by just watching it
a visual novel can be entire experienced by just watching youtube and just watching every ending. you can be a fan of steins;gate without buying the VN yourself because you will miss out on precisely nothing either way. this is why visual novels are not true video games.
