I haven't ridden on Space Mountain in DLP in a long time, but I remember it being a much, much, much smoother ride than the Space Mountain in WDW. I also liked it much more than RnR in HS, but that could have been the themeing. I think it's also a longer ride, but I'm not sure if that's just because the loading/acceleration occurs differently. The acceleration occurs going uphill DLP versus it going along a flat (pretty much right away) on RnR. I think RnR is shorter and easier, but very comparable in terms of how "tough" it is to ride. I LOVE Space Mountain in WDW, but these days it hurts my back a little bit--it's a lot of fun and the effect that you're going to "hit" the track as you swerve in and around it is very thrilling around what is otherwise a pretty tame coaster--but it's not really smooth at all. I think it's also much longer.