*** WARNING SPOILERS BELOW ***
Mass Effect 3
Shepard finds the intelligence behind the Reapers who gives some bs explanation about the synthetics having to destroy the organics to prevent them from being destroyed from the synthetics and offer him/her three choices: destroy all synthetic life in the galaxy, take control of the Reapers fleet or fuse synthetic and organic life together. No matter what is your choice, Shepard appears to die, the Mass Relays blow up leaving the rest of the galaxy in a new dark age and the Normandy is stranded in a wild planet. At the very end, its implied the whole story is being told by a old men to his grandchildren in a distant future.
Assassin's Creed III
Connor's storyline: Connor get his revenge against his arch-nemesis Charles Lee, but his mentor dies soon after, the Colonists are a bunch of assholes who force Connor's people out of their lands, rendering all of his efforts and actions to help everyone completely useless.
Desmond's storyline: Like Shepard, he is given two choices: let the solar flare wrecked the world again, becoming its own messianic figure to help the people, only for a whole new order of Assassins and Templars to arise and begin the whole war all over again or save it at the cost of own his life but unleash Juno upon it. Unlike ME3, you don't choose anything and he picks the latter option.
So which one is worse?