OK, I'll add my two cents. I am a long-time WDW veteran but visited DLR for two 4-5 day trips in recent years. Here are some of the major distinctions:
The Locals
The DLR locals are frequent and passionate visitors, and they know what they are doing (unlike most of the guests at WDW). They know all the tricks - the "secret" bathrooms, the best FP strategies, the best parade viewing spots, etc. Knowledge of good touring strategies is a must. The high percentage of locals also has some strange impacts on daily attendance - a random Tuesday in June may be much more crowded than a Saturday, for example, due to local AP block-out dates. But their ownership of the park is just amazing, and it helps make DL feel more authentic than WDW. On a Saturday evening, I sat and watched the swing dancers at the Carnation Plaza Gardens stage - these were people who had been dancing here every Saturday for decades. Meanwhile, over at the castle, there were two marriage proposals within the span of a 1/2 hour. You can really tell how much this park means to them.
New Attractions
New attractions are absolutely mobbed, even more so than at WDW (given the high percentage of local visitors). On my first visit, the Nemo subs were new and had consistent 2+ hr waits. On my second visit, Star Tours 2.0 was new: the FP ran out by 10:00 AM every day, and wait times were in the 75-90 min range. Likewise, the Little Mermaid ride had just opened at DCA a few weeks before, and consistently posted 60+ min waits. Meanwhile, the rest of the attractions were not neary this crowded. Keep this in mind for touring strategies.
Live Entertainment
Live entertainment at DLR is absolutely top notch. The daytime parades are actually worth watching, Fantasmic! is absolutely amazing, the Aladdin show is awesome, etc. Billy Hill and the Hillbillies are retiring this week but I loved them. I especially loved all of the street entertainment, which is everywhere - jazz bands in New Orleans Square, steel drum players in Adventureland, etc. Often you aren't hearing the area loops because you are listening to live bands - it's fantastic.
Size
DLR is very compact, making it very easy to criss-cross the parks. The smaller walkways make it feel crowded almost all the time, even on days when it is not particularly crowded. During the evenings, it is particularly a struggle to navigate the parks. At DL, for example, there is so much evening entertainment (the fireworks, F!, the projection show at IaSW) that the walkways are mobbed. The CMs institute crowd flow measures, like setting up strollers as a divided highway in Adventureland, or forcing counterclockwise movement around the hub, etc.
Design / Area Development
At DL park, there is a density and layering to the theming, from decades of development, which make it feel more organic and authentic. However, given DLR's small size, the transitions between lands are often lacking or non-existent. But what it lacks in grand vistas and cohesive transitions, it more than makes up in the details and charm. The trees are older here, and everything feels like its been here for ages. New Orleans Square and Fantasyland are thematic highlights.
DCA, on the other hand, feels a whole lot like parts of DHS and DAK. The make-over has helped enormously, but it still feels a bit incoherent to me.
Attractions
Much has been said about which coast has the better version of specific attractions. Some are identical to their Florida counterparts (mostly recent attractions, like TSM and the Little Mermaid ride), while most have some differences. I recommend riding all of the DLR counterparts to spot the differences and see which you like better. Some are significantly better at DLR, like Pirates. I also recommend riding some of the old-school attractions, like the Davy Crockett's Explorer Canoes and Storybook Land Canal Boats, which really give you a sense of the history of the park and let you marvel at how the lawyers haven't shut these down yet.
Queues
Many/most of the DLR queues are outside and unthemed. Waiting outside is fine, given the mild and dry weather. The elaborate queues at WDW (like Pirates, Everest, etc.) are missed. A notable exception at DLR is the queue for Indiana Jones, which is one of the best themed queues anywhere. And in some cases, the outdoor wait at DLR is greatly enhanced by the surrounding theming - such as at It's a Small World or at Alice in Wonderland / Teacups. And it is easier to estimate the actual wait time, when you can see the whole queue.
Weather
The dry, moderate weather in DLR is gorgeous compared to hot, swampy Orlando. However, it can get cool in the evenings. On my late June trip, I needed long pants and a jacket for the evenings - these can be easily stashed in the lockers midway down Main St. (much more easily accessible than those at MK).
Food
The food is generally good, but there are much fewer TS than WDW. My impression was that there were many more vegetarian/vegan options at DLR, and many of the dishes were infused with local California flavors (like avocado). For QS, much of the seating is outside.
Snacks
For you churro fans out there (like me), there's a cart in nearly every land. The Dole Whip stand is very popular (the longest line for me on one trip, at 45 min), but you can take the Dole Whips into the Tiki Room. In general, I think WDW has superior snack options - mostly because of WS.
Apologies for the long length. But I will say this: Disneyland is absolutely amazing, and you owe it to yourself to get out there and see it. Disneyland is by far my favorite park. It's where I've felt the greatest connection to the other guests and to the history of Disney. Walt was right: Disneyland is our land.
