Of course not. Bittersweet endings generally leave more of an impact than happy endings.
Saved the world, got the girl, everyone lives happily ever after is... fine, I guess. It works. But when the girl dies, or the world isn't much better off, or something happens, we find outselves remembering the story much better.
True art is angsty, after all. A "powerful" ending is most often one that makes you feel more sad than happy.
That said, it can be implemented badly, just like any other storytelling trope. You find yourself not caring, or there's no closure, or it feels like a cop out. "Rocks fall, everybody dies" is incredibly frustrating to the audience, much more so than any sort of "weak" ending that everyone expects.
This is the problem with straight out downer endings. It is extremely hard not to make them feel inconclusive or lacking closure. We know what happened, the hero lost. The world was destroyed. Bad guy won. But it takes a very, very skilled writer, a lot of luck, or a specific type of story/game to not make it feel like a bunch of bullshit.