Having just finished watching the first season - 1080i + 5.1 rips direct from DVR - I can imagine that the Blu-ray would look and sound magnificent.
If you've read the books, specifically Game of Thrones, some of the changes will eat at you, but those changes are overall eclipsed by the excellent casting. Some of the scenes not from the book seem to be there only as an excuse to show explicit sexual scenarios that serve no purpose. The CG used for backgrounds, castles, etc. ranges from mediocre to good, but never excellent. Some of the keys are terrible and really stand out - hopefully they fix some of the CG for the Blu-ray as they have had plenty of time.
Overall, I'm a fan and it does justice to the book better than most adapted works I've seen. I'm excited for season 2 and will likely buy season one on day one.