Wife and I were big WDW fans until they instituted FP+. We tried it, and it doesn't suit how we liked to enjoy the parks. We switched to DLR after that year and loved it!! Went back to WDW the following year to see if FP+ worked any better for us and it didn't. So, it's been DLR (and Universal Orlando) ever since.
The biggest thing is the lack of planning. Since you don't have to deal with making ride/food reservations and basically locking in your parks for at least part of your day you eliminate a huge part of the planning phase involved with WDW. Want to switch parks? Take a one minute walk across the courtyard between DL and DCA! Were you a pro at the old school paper fastpass? Well, you can relive those days at DLR. Want an even better experience? Try Maxpass and pile up those fastpasses for either park and from pretty much anywhere (once active, you can reserve fastpasses through the app from anywhere. We would take a break back to our hotel and secure at least our first ride back in the parks before leaving our room).
Cost is another big one. Unless you ABSOLUTELY must stay onsite, the plethora of hotels within easy walking distance is incredible and can fit any budget. The Disney "bubble" from WDW isn't really a thing at DLR and that's not necessarily a bad thing. There are also a ton of things to do in and around Anaheim (Knott's, Six Flags, Universal, Hollywood, Whale Watching, lot's of great food options). We had our last trip there late last year and it was a fantastic, stress free time. We rode everything multiple times, had some great food, and some other wonderful non-Disney experiences.
To be fair though, one of the only real drawbacks (if you rely on Disney Magical Express at WDW) is the need for transportation. It's a must to get the most out of your trip. We took a town car our first time, which worked well. But, it did limit the how much we could do outside the parks (Knott's Berrry Farm, though, is a quick bus ride from the parks).
You can check out our trip report for our last trip
HERE.