There's just a few differences...
Size: DLR's 200 someodd acres vs WDW's 28,000 acres
Size is where it starts because size allows for all the following differences:
Parks: DLR's 2 vs WDW's 4 theme parks & 2 water parks
Resorts: DLR's 3 hotels vs WDW's 20+ hotels
Things to do besides the parks: DLR's Downtown Disney vs WDW's larger Downtown Disney, Professional Golf Courses, Miniature Golf Courses, Wide World of Sports Complex, Boardwalk, & water activities.
It all starts with size.
-- PMM