Rhapsody in Blue and Rachmaninoff Piano Concerto no. 2

Hi, i`m learning the rhapsody in blue by gerswhin, and later this week my copy of Rachmaninoff`s Piano Concerto no. 2 in C Minor will arive. What I`m wondering is how much more difficult is this concerto than the rhapsody? And any practice tips/techniques for either of these songs would be appreciated.