There are 3 MAJOR differences:
1 - At DLR you have
Disneyland and DCA (which is a much smaller park, not comparable as a stand alone imho)
At WDW you have 4 stand alone parks and 2 water parks.
2 - You can very easily walk back and forth from DL and DCA throughout the day (several times) if you wanted.
WDW parks are much more spread out, requiring transportation to do so and more planning to make effective use of your time
3 - WDW is self-contained.
DLR not like this. There are the 3 hotels on property, but if you stay off-property, you can still be VERY close. You can eat across the street and walk "home." At WDW, you cannot do this. To leave the WDW resort is a "to do."
In my opinion, these are the biggest most basic differences.