I find the look of the new castles preferable to the system x ones (I was never a fan of the color scheme and thought it looked "unrealistic"). The new ones seem a little closer to the original castles, although the construction/system does look cheap. Nothing beats the steck buildings.
I am not a fan of system x, and with good reason. I was helping a friend's daughter put together 4190 Riding Stable, and I was so frustrated at how easily everything fell apart. And if an adult finds this frustrating, how is a child supposed to enjoy a building system that is so flimsy? I had a similar experience with Lego this weekend. My son and I were putting a truck together, and while we enjoyed the building of it, it does not stand up to play (especially from a younger child). My son ended up getting more and more frustrated with it as the pieces just kept falling apart.....how is that supposed to be fun?!!!!
I think that the more stable a buidling system is, the better, especially for younger hands. PM really had a great thing with Steck, and I don't understand why they got rid of it. Perhaps these new buildings are an attempt to correct the problems with system X, but they really just need to smarten up and bring back the Steck!!! So many problems (not to mention desires of the collectors) would be solved!! Shame shame shame!