This is my take as well. It was the right ending -- the problem was the last season should have been 2 (maybe even 3) seasons. I think the decision to "wrap it up" with season 8 was the network's decision for budgetary reasons? Can't remember.
The story I heard at the time was that HBO really did want to extend it to more seasons (why wouldn't they?), but the two show runners wanted to be done. They had recently signed on to a Star Wars show I believe.
