I just did this trip in July and it was truly amazing. You do backstage experiences and will ride some attractions as a group. We had an evening and two afternoons of free time in the park. Guides preloaded fastpasses on our accounts, the most was 5 for each of the afternoons and an additional fastpass for the arrival and departure day at DLR. I remember thinking "only 5 fast passes?" but we didn't even use them all; there just aren't as many FP attractions in DL and DCA. You might find them useful if you want to re-ride some of your favourites. This is with spending most of our free time touring the parks and closing out the parks each night after fireworks and World of Color.
While I loved this trip and can see why many people do it over and over again, I would not want this experience to be my first introduction to Disneyland. The trip is incredibly fast-paced and I would've felt much too overwhelmed if I had the expectation to see everything in both parks in such a limited amount of time. I think that one of the great things about Disneyland is all the little details that you need much more time to explore.
Though this is all my two cents. If you decide to go ahead and book the trip, you'll have an amazing time.