Man the first 3 books are freaking beyond amazing and GRRM is an author that actually has more realism in regards to deaths to main characters. There is way too many books where 90% of the main characters never die or miraculously recover from all wounds.
The deaths and fantastic plot/storyline changes is what makes this series stand apart from others- it certainly doesn't weaken it.
The 4th book is not as great but not as bad as some fans claim but there had to be a drop off after the first 3 amazing books and Martin split book 4 and 5 in half basically to concentrate on the events in King's Landing in book 4 and out of it in book 5.
They haven't even started filming season 3 as season 2 was just shot and edited for it's start next month. They will probably start shooting season 3 later on this year.