Best:
Killer 7: I love mind-frag shows and books etc. so when I got to the ending and all the pieces came together (yes, I'm one of those freaks that actually understood K7) , I was just awestruck.
Hitman: Blood Money: Best way to ring out a game - screw all that subtlety and Silent Assassin stuff - we're going out in a hail of gunfire and chasing down Crispin Freeman.
Worst:
90% of all NES games: Seriously, this was back in the day of passwords and battery back-ups were only to upper-tier games. You worked your ass off to get through the game and usually at the end you were given a single "Congratualtions, You Are Beat the Game!" and then roll credits. It taught a whole generation of children how to become masochists.
Dead Rising: There is no good ending. NONE.
WTF:
Borderlands: I would put this as a Worst, but as I understand it, Gearbox is shaping this game to be a game without an ending. Still, when myself and three of my friends haul ass for three hours straight and bust through waves and waves of enemies, working like a well oiled machine and finally getting to the end where there is no strategy, you just STAND THERE and pump lead into the final boss for two minutes and you win... eh... yay?
Fallout 3: This is to both pre Broken Steel and afterwards. The first because it was a triumphant, "Thanks for playing, Chief!" no matter which way you play the game. Yeah, the narration at the end changes, but still a nonchalant way to go. And post BS because.. there is no ending... unless you count going to Maryland and fighting off alien invaders an ending...