@Arliss: Yes, most of us are aware of the fact that there are constraints due to the budget, screentime, etc. and that some changes are necessary due to television being a different medium. No one is saying that the show should hve included all 3000 something characters from the books or that the show should have included each scene from the books. Having said that I think (and I believe many of the others here will agree) that the show could have done things differently with the same budget and the same screentime. Actually, I think the showrunners aren't using the screentime very well.
Here are just a few examples of how they could have done stuff differently with the same budget and the same screentime:
The show spend hours on showing female nudity. Especially in the earlier seaons. If I'm not mistaken the total of these scenes amounts to the lenght of several episodes. Apart from being sexist, most of them add nothing in terms of worldbuilding, character or story development. Cut them and you can include some scenes that are missing from the books. Cut stuff like the nearly 4 minute long beetle speech or Tyrion's cock jokes and use them better.
Again the show can't include all characters from the books, but still we spend hours of screentime with invented characters, some of whom were very unpopular with the show-only audience as well.
The fact that Lady Stoneheart is missing, isn't the only reason why I found D&D's stament that they miss Michelle Fairley pretty ironic. They underused her very much in Seasons 2 and 3. In the books Catelyn is the POV character with the 5th highest number of chapters, despite the fact that she had no chapters in AFFC and ADWD. On the show she has less screen time than characters like Talisa and Shae in Season 2 and 3 respectively. You don't have to add overall screentime to give more to Catelyn. Just cut brothel scenes or cut screentime from Shae and Talisa who shouldn't have that much.
The showrunners could have cut 2 of the 3 Sandsnakes who are only minor characters in the books and they could have cut Trystane who doesn't appear on page in the books could be cut as well give us Arianne instead of these characters.
Would I still thinks that the show sucks if I hadn't read the books? Well I'm not gonna lie of course the fact that I've read the books has influenced my opinion of the show and I've only been unsullied in Season 1. Having said that GoT already fails on it own terms when I don't compare it to the books. Furthermore, when I criticise the show on it's own terms I complain about the same stuff that I would complain with any other TV show or movie.
Edit: I wholly agree with what the orhers have said. Back in Season 2 there were some changes I didn't like and where I think they could have done things differently. However, my overall opinion of the show was still extremely positive. Like the others have said for me Season 5 and 6 were bad on their own merrits and by the time I watched I had forgotten a lot of stuff that happens in the books.