My wife and I honeymooned at WDW in 2011 (and I've been several times). We just did five days at
Disneyland this past September. My observations ...
It's pretty cool to be able to walk between both parks, Downtown Disney, and the Grand Californian at Disneyland Resort. That said, it's a LOT of walking (and standing!), and my dogs were really barking by the end of the trip. Yes, you don't have bus transportation taking time out of your days. But you also don't get that transportation break off your feet.
Speaking of, I couldn't quite get used to the fact that when watching stuff like Fantasmic or World of Color, you're either standing the entire time, or sitting on the pavement. It was not a comfortable experience. Outstanding shows, but it definitely didn't help after a long day of walking. (ProTip: We figured out that you could buy those "pillow pets" they have around the park, leave them in the bag, and sit on those for a bit of comfort. We gave them to our nieces as gits when we got home.)
Queues for most rides at Disneyland are outdoors, and if the weather is bad (wet, or too hot), it'll be a problem. I prefer the queues at WDW for that reason.
The Disneyland parks are smaller, but denser. There's as much to do in that small space as there is in all of WDW spread out. So you won't be lacking for ride experiences or entertainment. But smaller sometimes means that outside of a ride, the experience isn't as immersive. I went to WDW first, so it was a bit weird to be able to see other lands from within Adventureland, for example. They were more careful about sightlines at WDW because of the space they had to work with. At WDW I feel like I'm really someplace special. At Disneyland, as much as I enjoyed it (which was a LOT), I never felt like I was anywhere else but California.
You have a much wider variety of food at WDW (largely due to Epcot and the sheer number of hotels/restaurants) than at Disneyland. My wife (a vegan) complained often about the lack of choices. Our dinner at Napa Rose made up for it, though.
Ever wanted to sleep inside a themepark? You won't get an experience like that as inexpensively as a room at the Grand Californian. Our studio on the top floor faced Paradise Pier. We were able to watch World of Color from our room. (And saw them testing scenes from Winter Dreams in the middle of the night!) You really do feel like you're staying in a Disney park, and there's nothing quite like that (save for a handful of rooms) at Walt Disney World.
They both have plusses and minuses. WDW will always be near and dear to us, having spent the beginning of our life together there. But Disneyland was great, too. Any Disney fan should experience both.