After 30 some visits to WDW I tried my first visit to
Disneyland and California Adventure as an adult and definitely enjoyed the parks. DS wanted to see these parks and Hollywood / LA, so we did a mini trip. Note: I was in Disneyland back in 1964 too when I was four, but don't remember much from that.
The Disneyland park is really similar to the Magic Kingdom (I love them both), but I actually preferred the Disneyland park. My son did too. It was just so charming (had more of a fairytale land feel than the Magic Kingdom). Also (and we went at a low season time - January), there was a different vibe with lots of locals. I didn't see any meltdowns with exhausted kids and stressed out parent almost saying you will have a good time given how much we are spending on this trip. Rather I saw people who probably have season passes catering to what their darling little kiddos felt like doing. It was just so refreshing to see that. The California Adventure park was fine, but IMHO not as good as Epcot, Hollywood Studios, or Animal Kingdom.
We stayed offsite, but walking distance to the parks. It was really convenient / easy. As you don't need as much time to cover parks as you do in Orlando (we spent three night / two days and that worked well for us. We made it a split trip, spending some time in Hollywood / LA to see a few things there before going to Anaheim.
As much as I loved the Disneyland park, the Magic Kingdom is very similar and it's just so much more economical for me to go to Orlando (air and offsite accommodations), so I doubt I'll be back. Being able to stay offsite and walk to the parks is nice in Anaheim. The offsite accommodations were nothing all that great (clean but dated hotel type accommodations - a little shabby), but worked fine for a short stay. It's novel to be able to walk over, so I'd recommend doing something walking distance there and that does help make it feel pretty low key just to walk over and back anytime you want. In Orlando, though, you can stay in such nice updated condo offsite accommodations for such a great price, but you do need a car or need to do uber / lyft. And the condo rentals in Orlando are less money than the dated hotels in California. So they are just different types of vacations.
I honestly think you will enjoy doing the California parks and not be disappointed. The parks are really nice and enough different that it's really fun for a Disney fan to see similarities and differences. We think it was well worth making the trip. It does feel like a more low key experience too which is what you are looking for.
Next up for us: Disneyland Paris in September. I think we will enjoy that a ton too just like Disneyland California.
Again for us these one offs are super fun, but more a one time thing as they are way more expensive to get to. We living in the Midwest in the US have easy quick inexpensive direct flights to Orlando and relatives who live in Orlando too, making WDW a no brainer for where to most often go for a Disney fix. But Viva la difference -- tons of fun for the Disney fan to check out the other parks.