We all assume it's building to a happy resolution because we are used to that, but GOT has taught us better than that.

I can easily see them lulling us into seeing the happy ending and it not going that way at all.

I always imagined GOT not to have a clear ending as much as a "well this happened and the world will always continue" type ending. Something more along the lines of The Wire where we don't really get a resolution, but just an ending for the show with the message that the cycle will always continue.