I think the neatest thing about DL is that when you are there you almost 'feel' Walt's presence. It is so neat to know that he walked those streets. Way back when, I was a cast member for WDW and was sent to DL to help open DCA. One of the most awesome things was guest relations taking our small group on a tour of Walt's apartment above the firehouse in DL. Everything was just as it was back then, again, it felt as if he was there.
As everyone else said, they are totally 2 different parks. DL is much smaller, my first thought was - Where's the castle? But then you realize that everything is smaller, the buildings, the train, etc.
I love DL at Christmas time, how they have It's a Small World lit up is JUST like they show it on Soarin' (which came from DCA btw).