Eight seasons does sound like a lot until you consoder that due to the low number of episodes per season, it's still a really low amount compared to many successful series out there. Considerably less than the likes of Lost, which went on one season too long. There's a lot more happening in this show than there is in Lost, at least in my opinion. I think it'll probably become more understanding as they wind things down and a climax actually looks like it is in sight. There are just a *lot* of things I still want to see happen in GoT and I don't know that they could give them all enough time to put them all in. I get that feeling that we're about half of the way through a story at the moment. Mostly because omg Dany get to Westeros already. Or at least out of the bay.
I can't think of the last series that would go far into a sixth season with over double the ratings they had for the first season. This show is such a huge success and I just don't ever watch a show and think "Man, this show is getting meh". I'll probably be kinda sad when it ends.