If there was a misstep in His Dark Materials, I'd say it was The Amber Spyglass. Not that it was bad - far from it - but it didn't have that same sense of majesty, the story wasn't as gripping and as flowing, as in Northern Lights and The Subtle Knife. It's generally a bit more scattered, while creatures like the Mulefa will be difficult to adapt convincingly (four-legged wheeled animals, with one leg at the front, one at the beg, and then one on each side). Hopefully they can do that, and also pull it all together into a slightly more focused piece of work. The end battle is something that can hopefully play out well on screen too, and they can make it into a truly epic war (provided they, y'know, have the budget).