DL is a wonderful place (not that WDW isn't), but it truly is special. WDW wouldn't exist without DLR!! By itself, DL would basically fit inside of the parking lot of Epcot... when you factor in DCA, DTD and the hotels, the entire DLR would basically fit inside of the entire Epcot complex - or pretty close it.
You will find that DL, compared to MK, has a very DENSE line up of attractions and experiences. There are something like 80 or 85 things to do inside of DL, whereas MK is closer to 35 to 40. Most of the attractions that you are familiar with at WDW originated at DL - and many of them are considered to be superior versions at DL...especially POTC - but some did originate in FL and made their way west. If you've experienced Soarin' at Epcot - it orignated in DCA. Whereas DCA got a version of ToT, but is lacking DHS' 5th dimension room. Pretty much there are few truly "unique" attractions at DL... the Matterhorn Bobsleds (the first iron tubular roller coaster - rough, but tame as coasters go), Alice in Wonderland, Indiana Jones in Adventureland, Roger Rabbit's Cartoon Spin, Davy Crockett Explorer Canoes (pictured in my user name info), Finding Nemo Submarine voyage, and a few others that I can't recall at this moment.
The entrance gates of DL and DCA are literally a few hundred feet apart, so you won't have a lot of need to worry about transportation between them! It's just a hop, skip and a jump away and you can park hop. This makes it very easy to spend time in both parks in the same day, without planning on about an hour to get to your next destination.
The weather in So. Cal is great most of the year. Humidity is not a major concern, as it is in Florida. If it rains while you are there, that is truly a magical time to be in the parks. Many people leave, or simply don't show up - and you truly can feel like you have the park to yourself. Unlike FL, however, a lot of the queues are outdoors, so if rain is in the forecast, you'll want to have a poncho or umbrella. The summer months, through Sep, can be very hot. Many times getting over 100. The spring and fall can be quite pleasant, getting cool in the evening hours.
Since the resort is much smaller, there aren't as many dining options. DL has some great restaurants, DCA not as many. The Blue Bayou is wonderful, both in atmosphere and food. It's inside POTC, although it has it's own entrance within New Orleans Square.
Two of the three hotels at DL are very different than anything found at WDW - only the Grand Californian is similar, since it was designed by the Imagineers - the lobby feels very much like WL and the GF. The
Disneyland Hotel dates back to around 1958 and was built by the Wrather Corporation, purchased by Disney in the '80's ... and even though it has been refurbished and updated, is a general hodge podge of growth through the years. The Paradise Pier hotel was built by others, and purchased by Disney in the 90's. I've never seen the PP hotel's pool - but both the DLH and GCH have very nice pools.
If and when you do go - remember that there is "extra magic" at DL, since it is the only park that Walt ever walked in. His apartment above the firestation can still be seen (though actually getting into it is not something to count on), and the current Dream Suite is housed in an apartment suite that was designed for Walt and Roy to entertain VIP's in - but never occupied by them since Walt died before it was completed. Before the Dream Suite concept came along, it was used as the home of the Disney Gallery for 20 years, selling all kinds of beautiful Disney artwork, like they sell at DTD at WDW, and in the MK.
In the end, you could safely plan a trip for 3 days and feel comfortable that you have enjoyed it all - but of course 4 days would be better. DTD at DLR is much more compact that at WDW, but still hosts some great shopping and dining. Rainforest Cafe is there, as well as House of Blues, ESPN Zone and others.
Lego, Starabillas, AMC theatres, Basin, Wetzel's Pretzels are there too - just like in FL. And then there are many others.
There are lots of good hotel options surrounding the parks. Many are right across Harbor Blvd within walking distance, or just across the street and around the corner.
I hope you get to go - and have a wonderful time!!
. That being said it is NOT WDW! You do not need a week to see it all. We never need more than two days, three if we want to go back and see things again. There are no water parks, mini golfing, dinner shows or the great choice of dining. We love 
.......... but we will have to see because the CA reno should be totally done in '12......... so who knows when i will actually get to WDW lol........... maybe i'll find a cheap package between now and then lol
but at the very beginning of school they don't seem to miss much and can make up what they missed. The weather is great in early Sept. Not too hot, not too cold. We are also trying early Dec. this year. A little colder, but wonderful decorations.
