Eh, they could have added more stuff and had it not be too much, especially in Flotsam where the game didn't have as much urgency at the time. ›››
Ye see, that's something I like about The Witcher, and what was basically crumbled in the final act. Rather than being set along to your goal with the utmost urgency, or even knowing exactly where your going, the idea is rather to take the environment on a holistic and meaningful level. The fact that you're not trying to climb a mountain to reach the bad guy or walking through the town with murderous intent is refreshing. The world adapts around you because things are hidden directly from your eyes, and occasionally you have to face a roadblock that you cannot directly overcome at the current time. That, I think, is the power of the series in design. Even with things like the threat upon Vergen and the Kaedweni camp in Act 2, that served more as the overarching goal than a definitive problem to be solved immediately.
An open world could both help and hinder this. You certainly never want a game to seem completely undirected, since it limits the chance to actually take in the world and its breadth. Open worlds can rather help you understand things as it relates to your timeframe by giving you a concept of what is at stake. The Ultima games do this the best out of any RPGs in existence, primarily Ultima 4 (at least, in my opinion, as others would point to U7). They create an exciting world with a wide variety of goals in order to overcome the central threat, which is dangerous, but ultimately only becomes a threat once you confront it. This justifiably allows one to take their time in order to prepare facing that threat, and to change the world as they please. I think the Witcher's design is all ready conducive to a proper "open" way of world interaction with its wide open levels, but a properly designed open world could allow the story in general to breath more. Primarily, I think it could help with things not being so coincidental, like meeting the people you're meant to arm wrestle directly in the next chapter, rather doing it within the same continuous world.
I'm excited to see what will come of it, but I hope it's more directed than it is merely 'open'. I like the Elder Scrolls games, but those games are ones that reside on the moments of respite and taking in the world visually, since the story as a whole is ultimately banal. The Witcher is the opposite, where you're excited to reach the next story opportunity rather than exploring the environments, as nice looking as they may be. Here's to a proper design work, and CD Projekt's aspirations!