I knew this show was going to be the next 'Lost', so I never invested in it.
You just simply cannot take a zombie survival horror movie and stretch it out into a long series.
I've been telling people this for years now.
Addendum: While I've never particularly felt that Game of Thrones was too long for it's premise, I don't watch that show either. I'm just not really into "medieval" fantasy stuff.
I haven't watched a series since Nurse Jackie, and even with that I gave up after the third or fourth season.
There are very few shows that I've watched start to finish.
Well, if you don't count animes.