It's pretty good. Season 9 almost killed the show for me, but season 10 is off to a good start. It can get repetitive/boring, but it does keep your attention in most places. It's not great, it's not terrible, it's just pretty good. I recommend only watching the first few seasons and then pretend they all died or found salvation, because the later seasons aren't that good.
Edit: it used to be a 3 star rating but I'm giving it a 4 star out of respect for the twist at the end of the 12th episode of season 10.