Yea, Riku mode was all about beatin the crap out of people, and Sora's was all about the story and emotions, and all that good stuff.
Plus, it was a lot longer. Sora mode took me 22 hours, and RIku mode took me 10. Which is awesome considering that I beat KH in 16 hours my first time. They did a good job making this game longer and more fulfiling.