After numerous trips to WDW, we decided to head west to DLR this past March.
We loved it!!!! 
It really is hard to compare the two even though they share some of the same rides. There are some rides we liked better at DLR and some better at WDW.
Here's my comparison (mind you, this is my OPINION):

Haunted Mansion - WDW Better
Pirates of the Caribbean - DLP Better
Dinosaur/Indy - DLP Better
It's A Small World - DLP
ToonTown - DLP 10xs Better
California Screamin' vs RNR - RNR Better
Space Mountain - DLP Better
Buzz Lightyear's Astro Blasters vs Buzz Lightyear's Space Ranger Spin - DLP Better (You can actually take the laser gun out and move it around semi-freely. It was easier to shoot that the MK version.)
Downtown Disney - DLR Better (They need to put a BAB in DTD Florida. The smaller one in T-Rex isn't cutting it. The DLR BAB was BUSY!)
Okay now looking back and the ride comparisons, I think we liked DLP better than the MK.

However, the rest of the DLR resort can't compare with WDW. It is like night and day. They are two totally different resorts when comparing the size, hotel offerings, transportation, number of parks and restaurants. After visiting DLR, we still love our WDW and plan to continue going back year after year. With a few "side trips" to DLR.

DH and are I going back to DLR in April 2010. Also, we may try and squeeze in a December 2010 DLR trip to catch the holiday decorations and see the Nightmare Before Christmas Haunted Mansion.
Personally, I think any WDW and Disney fan should visit Disneyland California at least once. It's where it all started afterall.

Jennifer
(FYI - I did a Trip Report for our DLR trip if you want to read it click
HERE.)