I just finished the game....aaannnddddddd...if your on the fence about getting it...
DON'T
And if that didn't convince you, you are already lost.
The Ending was the lamest excuse for the conclusion to a trilogy ever. the choices you where given are crap, to say the least.
I always liked the ME series because it was grounded in reality, no spirits or divine intervention or any crap like that, just a technical shootout with big aliens and evil groups. I won't spoil it, but you don't get to kill Harbinger. Its really un-fulfilling. Its like having sex then your partner just leaves before climax.
Power does not corrupt. Fear corrupts... perhaps the fear of a loss of power.