A few posts above Alex2kMommy was kind enough to recommend my DLR Guide for WDW Vets. I discuss there many of these issues, but here are some nutshell obserservations.
I think the biggest risk lies in your expectations. I have seen DLR people make their first visit to WDW, and vice versa, and they expected more similarity than actually exists. For some people the differences can become a disappointment rather than something to be enjoyed. If you let DLR be DLR, and not try to force it into being WDW, it will be a great experience and will approach or maybe even surpass your WDW experience.
One of the best examples of misapplied expectations relates to castles. At MK the castle is truly spectacular and is the central landmark of the MK park. The castle at DL is one-third the size of the one at MK and not nearly as grand. It is not uncommon for a WDW vet to enter DL for the first time and be immediately disappointed by the castle. When one of your first experiences is one of disappointment then DL has to really play catch up to MK.
However, what a WDW vet often does not understand is that a DL vet does not consider the castle as the visual landmark of the park. It is obvious to DL vets that the Matterhorn mountain, adjacent to the castle, is the visual landmark. When I was a child it was always a family game as we approached DL in our car to see who would be the first one to catch a glimpse of the Matterhorn. I have since learned that many other families had a similar game.
Therefore, a WDW vet who brings the MK castle expectations to DL may be let down, but one who understands that at DL the Matterhorn is the important landmark may be lifted up, especially since MK does not even have a Matterhorn. By understanding some of the WDW vs. DLR resort differences and keeping a reasonable check on your expectations, each resort will offer the maximum enjoyment.
On a final note, I agree with "Robert and Kelley" that if you liked MK and MGM Studios the best at WDW, you are the most likely of all WDW vets to like DLR - since DL and DCA have a similar feel to MK and MGM. In fact, that is probably why I enjoyed MK and MGM Studios the most at WDW during my first trip there earlier this year.