Since ME3's ending is being discussed quite a bit here, I just want to chime in with a paragraph or two (or three).
The moment they abandoned the original (and actually foreshadowed) "humans are special to the Reapers" and "Dark Energy is doing nasty things" ending, it just wasn't possible for them to put together a coherent ending without contradicting their expensive marketing campaign. When the war was all about the Reapers turning humans, and humans alone, into new Reapers, it made sense to have a final confrontation on Earth.
They just couldn't abandon having the climax in London, because too much development time and marketing money had already gone into making that an integral part of the endgame. So in the end we got the Crucible arc, the Reapers moving the Citadel to Earth without explanation or justification, and an entirely new motivation for the Reapers themselves finally barfed out in the last few minutes of the game. (Also, a Citadel interior that looked nothing like the Citadel interior, and a Conduit that seemed to exist for the sole purpose of beaming people into a corridor with quick access to another set of master controls for the Citadel.)
And, of course, on top of that there's the complete disconnect between previous actions and the events that transpire in the endgame.
The moment they abandoned the original (and actually foreshadowed) "humans are special to the Reapers" and "Dark Energy is doing nasty things" ending, it just wasn't possible for them to put together a coherent ending without contradicting their expensive marketing campaign. When the war was all about the Reapers turning humans, and humans alone, into new Reapers, it made sense to have a final confrontation on Earth.
They just couldn't abandon having the climax in London, because too much development time and marketing money had already gone into making that an integral part of the endgame. So in the end we got the Crucible arc, the Reapers moving the Citadel to Earth without explanation or justification, and an entirely new motivation for the Reapers themselves finally barfed out in the last few minutes of the game. (Also, a Citadel interior that looked nothing like the Citadel interior, and a Conduit that seemed to exist for the sole purpose of beaming people into a corridor with quick access to another set of master controls for the Citadel.)
And, of course, on top of that there's the complete disconnect between previous actions and the events that transpire in the endgame.