If I had to say one thing, Episode Duscae didn't seem to tell a story of any consequence. Where as, your average Witcher quest, which has a similar scale as the Behemoth quest would tell an interesting character story that had a proper beginning, middle, and an ending. So from that perspective it was a bit lacking from a story standpoint. Platinum almost had a story. I think if it was more substantial and satisfying, like say the kind of content we see in Brotherhood, people would probably enjoy the demos more.
That said, the density of content is just right in my opinion. Roughly 3 hours of content for that small area is plenty. I think most people probably spent too much time looking for more content after they already consumed the content that was there. In the final game you can move on after that and seek more content so it shouldn't be an issue.