I've finished it.
People are annoyed by the ending as your choices don't have that much effect on it. Without giving too much away, there are three main endings, and you choose which one in the final moments of the game. And it's amazing. I loved the ending I picked, I thought it was brilliant. And the choices you make in the game are important, the shape the journey, and how you ultimatly get to your ending.
The way I look at it is this. The game starts the same for everyone, and is going to end the same for everyone (There will be one ending that is considered 'canon' and the official ending). But that's not what is important, as everything you do, between those two points is the important part, how you get to the ending, what decisions you make along the way are going to matter, going to change how you do things, who is alive, what conversations and friendships and such you make, and get to have in the final hours of the game. That's what is important, not a cut scene that lasts a few minutes. Also I'd imagine the way you played the game and the choices you made are going to effect your decisions towards the end.
The game is fantastic, it's a brilliant 30 hours (with DLC complete and all side missions) and I'll be playing it at least once more!