Changes to the book can be extremely hit or miss.
For the first half of Jon's story this season I thought they kinda dropped the ball. Mance wasn't given enough time to flesh out, nor were the Wildlings. But after Kissed By Fire, I liked most of the changes, particularly the final scene between Jon and Ygritte, which wasn't in the books but puts a nice period on that storyline and relationship for now.
I liked the Brotherhood meeting Melissandre. Not in the books, but gives the readers a new and interesting interaction.
Didn't really like the emphasis on Robb and Talisa at the expense of Catalyn. Baby Eddard felt like a easy way to make the Red Wedding more brutal. (which it's really not, way more brutal in the book.)
Just some examples.