Dave of Canada wrote...
This is frustrating me as someone who loves bittersweet endings, you have to stop using Mass Effect 3's ending as standard for bittersweet and being so traumatized by it. It was poorly written, it has little to do with the actual content of said ending.
Here's a minor list off the top of my head of bittersweet endings to compare with:
GTA4, Silent Hill series, Shadow of the Colossus, LA Noire, Max Payne 2 (didn't play 1 or 3), Shadow of the Colossus, Dragon Age: Origins, most Final Fantasy games and spinoffs, Planescape: Torment, Warcraft RTS series, Diablo 1 and 2, Starcraft 1, Metal Gear Solid series, Half Life series, The Darkness games, BioShock 2, Red Dead Redemption, NiER, Batman: Arkham City, God of War games.
Most of these are critically acclaimed and praised for their stories, you don't hear "BITTERSWEET SUCKS" every five seconds when there's discussion about these games and their stories, you hear about how the endings really touched the player and impacted them.
The only difference is that badly written happy endings are tolerated because the player still feels warm and fuzzy, dismissing everything else about it because it caters to their "feel good" side. Look at half the people who's biggest complaint for ME3's ending was they can't have "blue babies" with Liara but then praised the EC when it implied they'd meet again.
Hypothetically, what if the Chantry ending was bittersweet and the mage ending was happy, at least for those who liked mages? You'd consider the mage ending inferior regardless so wouldn't feel as though you were handicapping yourself by picking the templar ending and would still get to enjoy that, and most of the people who want a happy ending seem to prefer the mage side, just as the ones who want a bittersweet one prefer the templar side, so everything'll work out.
Also, of the games you mentioned, the vast majority of them have preset characters, not characters that the player makes themselves and hence becomes personally invested in. As for DAO, I never found the ending to be bittersweet at all, but pretty much straight-up happy (though I didn't romance Morrigan... but a happy ending for that comes around eventually).