I enjoy these (as heart-wrenching as they are) so long as they aren’t overused in that particular game. (For example, you have six companions, but each pair has a ‘choose one of us and leave the other’ situation). Though not a CSG, Dragon Age (particularly Inquisition) has choices where you have to choose to save either the player-character of the previous game or a past (potential) love interest.
I think this is fine so long as there are also ways to avoid it: as in, one particular set of choices or gameplay may lead to the RO’s inevitable demise or sacrifice, but the story doesn’t always lead to that. Otherwise, deliberately offering a character for the players to fall in love with, knowing that they’re doomed to die no matter what, feels somewhat cheap (or cruel) to me. In that case, I’d be very turned off (but only in the case of interactive fiction).
I think it depends on the story, genre, details, world, and setting. If the game starts off bleak and ends bleak, it’s not a huge surprise that everything isn’t roses-and-puppies by the end, because not everyone can be equally happy and not everything can just suddenly turn from dystopian hellscape to fluffy perfection. However, I would personally feel cheated if the MC/other characters were put through the ringer–trauma, torture, horrific war, etc.–struggled, persevered, and overcame, only to have a ‘realistic’ ending where no one is happy and everyone has lingering trauma that never really goes away… I wouldn’t be happy with that. (cough Hunger Games, cough)
I think it just depends on the degree of ‘unfair suffering’ and who is receiving it. It’s okay if some people (ideally not the MC) don’t get a happy ending at the end of the story, especially due to their past actions or mistakes that were out of MC’s control (all the side characters who died at the end of Harry Potter, say). But if there’s no ‘good’ ending at all, only endings where no one ends up happy, I would ask: what’s the point in playing?
I’m okay with player character sacrifice as certain heroic endings, but not necessarily okay with it being a requirement for “the best ending.” If the player character is dead, it isn’t a “best ending” to me, because they’re not around to enjoy it! But I do think it’s possible to achieve good endings in a way that demands player sacrifice. I think the ‘best’ ending, if it canonically exists, should be extremely difficult to achieve but manages to keep the protagonist and company alive, perhaps through near-perfect stats or choices. Otherwise, if they have to die, that’s actually a bad ending to me, and I’ll be looking for a way to undo it.
As @resuri08 said, Dragon Age: Origins does a very good job with the ideas of sacrifice. You have to sacrifice something to get a good end. Whether it’s the player’s life or something else, some sort of toll is necessary–but the players get to choose what that is.
If you haven’t played them, the Telltale brand of narrative games utilizes these choices a lot. The Walking Dead: Season One (which requires no pre-existing knowledge of the franchise) has lots of “lesser-of-two-evils” choices where you have to choose which person to save and which person to sacrifice, which exit to run to and which room to leave unexplored, and these can have very long-lasting consequences throughout the story. I would also recommend “The Wolf Among Us” as well!