It's hard to believe that it's been ten years since the uproar of the Mass Effect 3 ending controversy. For those who were fortunate enough to miss it, the crash course version is that after dozens of hours across a sprawling RPG trilogy, the ending of Commander Shepard's epic came down to a relatively simplistic trinary choice that was almost wholly removed from the player's journey up to that point.
It's difficult to overstate just how big a deal this was, not just for Mass Effect fans but on gaming culture as a whole. The blowback was fierce enough that BioWare actually released an Extended Cut DLC aiming to provide "more closure with even more context and clarity," and an ending that "will feel more personalized for each player." It was definitely an improvement, but the outcomes were still rather grim.
That's where the Mass Effect 3 Happy Ending mod comes into play—and if you don't want to be spoiled, I suggest you stop reading here, because they're coming. The mod makes a number of changes to the big finish of Mass Effect 3 by canonizing a specific ending, cutting some content to make the narrative work, keeping the geth and EDI alive, and of course ensuring that Shepard survives and is reunited with their crew—including their love interest.
The original mod is still available, but unfortunately it's not compatible with the Mass Effect Legendary Edition. The good news for people who enjoy happy endings is that a reworked version, called Audemus' Happy Ending Mod, is—you can snag it now from Nexus Mods.
Audemus' Happy Ending Mod is described as a "spiritual successor" to the original, and is actually closer to JohnP's Alternate MEHEM mod, a rework of the original Happy Ending that incorporates the Extended Cut content. But the net result is essentially the same: It eliminates the Catalyst, preserves the Citadel and Mass Effect Relay Network, and of course keeps Commander Shepard—and their love interest, if applicable—alive.
It's also been designed to incorporate a Legendary Edition-compatible version of the Citadel Epilogue Mod, which turns the outstanding Citadel DLC—"a sweet, funny goodbye hug for long-term fans of the series"—into a Mass Effect 3 epilogue. The makers of Audemus' Happy Ending Mod are currently working on that and expect to have it out later this year.
Personally, I don't think the conclusion of the Mass Effect trilogy was quite the crime against humanity that some players made it out to be. A little disappointing, maybe, but not nearly enough of a letdown to negate countless hours of entertainment in one of the most wonderfully well-realized sci-fi universes I've ever encountered. That said, I do very much prefer happy endings over sad ones, and I think that if I ever get around to playing the Mass Effect Legendary Edition, I'll likely do it with this mod installed.