Undertale - The writer just failed for not including this one. Both the total good and the total evil ending are just
perfect. But I won't spoil them here. If you wanna see 'em just google it. But the best part of this ending was...
Fable - Because I was rewarded with the most awesome badass sword I've ever seen in a fantasy RPG if I chose evil and... Nothing if I chose good. Oh sure, you save your sister and all of Albion and whoop de doo, but you, the player, don't actually get anything out of it at all. I like that. Sometimes being good requires passing up incredibly tempting opportunities that will not come again. Not including TLC because that was added in AFTER the fact.
Halo: Reach - While most of the campaign was pretty meh for me, the ending knocked that shit OUT OF THE PARK. I could not have thought of a better farewell to the Halo series for Bungie. Kudos and massive props to them. And then Activision came... RIP Bungie. I'll miss you... There will be another time.
Far Cry 3 - You wouldn't think it but I found the ending to this game pretty cool. So think about this. The whole time, you're getting led around by the nose. Whether through forced cutscenes, main protagonist stupidity, or anything in between, it doesn't matter. You've had no actual control over the way things are panning out. And it goes like this throughout the entire game. But when you get to the very end. When you FINALLY get to that point. Your control has been restored to you at last. And in one beautiful moment. you can finally intervene and make the madness stop there or give in to it. And that, my friends, is genius. And as if that wasn't enough, the good ending shows you finally getting off that island with that dagger tossed into the sand with the sunset streaming gently across the island mountains. <3 Also, play this with Ziggy's Mod. Kthx
OK, lightning round now.
Portal 2 - I didn't think much of this ending when I heard about it until I actually played the game. And now it seems so epic. A good ending for Portal.
The Stanley Parable - Almost all of them at very least gave me a chuckle. Loved it.
The Beginner's Guide - Barely escaped these theoretical depths of madness with my sanity. Would get mindfucked by Davey Wreden again. 10/10.
The Legend of Zelda: Ocarina of Time - Besides Undertale's good ending, one of the best feel-good endings of all time.
The Legend of Zelda: Twilight Princess - "Holy crap, you're so beautiful... WAIT WAT R U DOING? Noooo...
"
The Talos Principle - Prove you're human.
Castlevania: Aria of Sorrow - Specifically the bad ending. See avatar.