I had mixed feelings about the Battle of the Blackwater. I do think that having this episode focus solely on the battle was the right thing to do. It's the climax of A Clash of Kings. However, I also understand the compromises that had to be made in order to translate this for the screen. Budget has been a significant consideration for the series, and this was no doubt the most expensive episode of the series to produce.
The show definitely changed some significant things: no catapults shown or mentioned. No chain across the Blackwater. No barges to make a bridge from one bank to the other.
There were definitely some liberties taken with Stannis. In the book Stannis was across the Blackwater from Kings Landing, waiting with the bulk of the forces. Ser Davos was on one ship, and two of his sons each commanded a ship. The change of Stannis leading the assault on the walls was not in the book. And the show put Davos and Matthos on one ship, and the other son never came to light.
But I think some key things made it in. Notably, the Hound's story. I think that Rory McCann has done great work as the Hound. And Sansa has come into her own in a big way. Oh, and what about Tyrion? Peter Dinklage has been doing an amazing job bringing this character to the screen. And when he was wounded in the battle? It was fantastic to see Podrick come to his aid.
Oh, and the wildfire explosion? That was a lot more spectacular than I had imagined it!