Not the same rides
One of the bigger and more regrettable mistakes a WDW veteran can make in Disneyland is to figure they can skip things like Pirates, Haunted Mansion, or It’s a Small World as those attractions are in Disney World as well. The reality is almost every Disneyland ride is different from its Florida counterpart. Big Thunder Mountain has a different layout, including a unique finale, while Pirates is far better in California.
California’s Fantasyland has always been fantastic and elaborate compared to Florida. Before it closed, Splash Mountain had notable differences, and Small World stands out by using Disney characters in the ride. There’s also the Haunted Mansion with extra rooms, and Jungle Cruise has unique scenes too. Some carbon copies exist, like Rise of the Resistance, but even if you’ve ridden Space Mountain a hundred times in Florida, it’s worth trying it out in Disneyland too.
Lots more locals
This is an underrated but important aspect of a Disneyland visit. Disney World tends to attract a ton of guests from around the country and the world, and a good mix there. Disneyland does get those same guests, yet it’s common for a majority of folks in the parks to all be from California. Disneyland is almost like a Six Flags park in that it’s easy for people in Southern California to head there for a weekend, with some Anaheim residents making it practically a weekly trek. Thus, expect a bit more local flavor with folks who know the parks in and out able to cut you off at times.