I've been to both DLR and WDW several times and they are very different vacations. DLR has always been shorter trips (2 to 3 days), while WDW are longer vacations (10+ days). WDW is designed to be an all encompassing experience - if you don't have a car, you probably won't see the "outside" world for the rest of your trip. Whereas at DLR, the "outside" world is very close and pretty hard to ignore.
The Magic Kingdom and
Disneyland are the two most similar parks, but even they are different. DLR has much more crammed (in a good way) into it than MK, which feels more spread out. Some of the rides are very similar, but may have some small variations or different outer looks. DCA reminds me the most of DHS, but not a lot. DLR does not have anything like Epcot or Animal Kingdom (AK). Epcot has two halves - Future World and World Showcase. The front half (FW) has lots of rides, whereas WS is mostly shopping and eating (there are a few rides). Animal Kingdom has some rides, but the main attractions are the animals.
Unlike DLR where you can easily walk from DL to DCA to DTD, none of the parks are really within walking distance (except DHS and Epcot, but it's still about a 20 minute hike). There is transportation between the parks, so it's not hard (perhaps time consuming) to get from one park to the next.
Essentially between the two parks at DLR and four parks at WDW, you'll find some rides that overlap (but are in different places - for example, Soarin' is in DCA at DLR and Epcot at WDW, but is identical in terms of the ride itself) and other rides that are only in one place (for example, DLR has the Matterhorn, but AK has Expedition Everest).
To me the biggest difference between the two resorts (aside from size) is that WDW has a lot more eating options. If you like to eat, then there is no shortage of places to try (especially at Epcot). There are also a lot more hotel choices (at all expense levels).
As PPs have said, if you've been DLR, but not been to WDW, then I think it's worth try WDW at least once. However, that being said, I think WDW is a much more expensive vacation (mostly because it's longer).
On a side note: the Dole Whips at WDW are different from the ones at DLR. I think it has to do with the dairy content, but between the two, I liked the ones at WDW better. You can get the Dole Whip at Aloha Isles (in the MK) and at Captain Cooks (at the Polynesian). Just thought I'd mention this because of your handle.