Welcome to the DL boards!
Those of you who are planning a trip to DL for the first time...please please please read Hydroguy's stickey! It's the best info out there for newbies and WDW vets.
I do not think you will be disappointed at all. DL is way more charming than the MK. More attractions, better detail and the rides tend to be better. The weather is also great. No humidity.
What you will be disappointed in, is the castle. Sleeping Beauty's is very small, compared to Cinderella's. DL's icon is the Mattterhorn. Also the Disney immersion is different. If you are worrying about this, then stay onsite, and you never have to go out into the real world once there.
Everything is connected. DL, California Adventures, DTD, the Grand Californian, the DL Hotel and Paradise Pier. All walkable. You can walk back and forth from each park if you like!
As for renting a car. Are you going anywhere else besides DL? The beach, San Diego, Hollywood? If so, then I would rent a car. If not, there is no need to rent. Just hop on one of the shuttles.(We can tell you more about those if decide to take one.) But if I were you, I'd take some time at least to see the beaches and San Diego.
I hope you are planning this trip after the World of Color has opened. It is supposed to be the best night time show Disney has ever produced. I can't wait to see it!!
Have fun planning!
