Speaking as a book reader
There were many changes tonight. Almost every storyline was at least tweaked.
None of it should ruin anything in the show. Almost all of it was to set up or clarify character motivations.
That's not to say that I liked all of the changes. But I understand why they were made and they're pretty much in the spirit of the books.
I'm more concerned with some things that are missing than things that are changed, but I know they pushed back some stuff til season 3, so hopefully they manage to handle that stuff well when they get to it.