I have only played Race for the Galaxy a few times and, while I was impressed with the game's design, it left me feeling a bit "bleh." I don't know if it was entirely an aesthetic concern, but I felt that something was missing.
My first play of Roll for the Galaxy, on the other hand, left me in a state of post-game bliss with a desire to play more. People always said that the joy of Race was learning new combos, attempting new strategies, and trying to make the most of what you were dealt. I think that Roll does similar things, albeit in a bit more streamlined fashion.
What's better is that it has been much easier to introduce this game, with its shiny dice and cool tiles, to new players than it was to get people to want to play a Euro-esque card game.