If I can't even get through a show due to disinterest, that is enough to base judgment on. I didn't find it to be captivating or entertaining enough to warrant watching the entire series. I can't objectively judge the acting/writing/characters over the entirety of the show, only the parts I have seen.
I don't think this is true, personally. How easily something initially takes to grab my attention ends up being a pretty insignificant factor, when all is said and done, IMO. They are definitely hurdles that affect whether or not someone is going to bother trying, but once I jump over them, they don't really matter, I find. (and they don't really re-appear on a second viewing after the show's won me over)
All my favorite things had hurdles, and most of the things I've tried that didn't have any, for whatever reason, don't manage to reach those heights. And after a while of noticing that pattern, I start to notice and be actively annoyed by the gimmick of shows trying too hard to desperately grab your attention right away, and tricking you into being engaged/addicted/hooked week after week (the way shows like Breaking Bad or Game of Thrones do).
I think of it as a factor that somewhat clouds judgement rather than contributes to it.
(this isn't me trying to convince you not to think GOT is good, btw-- I've just never agreed with the validity of that specific reasoning)