We have done one
ABD, with our second this coming summer. I loved it for the following reasons:
1. My family are not joiners and pretty severe introverts. I am the opposite. It was great to have others to talk to during the trip, who were not random strangers (which is who I normally have to talk to after a few days traveling alone with my husband, god love him). And it worked for everyone. My kids generally didn't have to get too chummy with the other kids, and my DH could just rely on me to do the talking in adult groups, as is typical. And I was happy.
2. I didn't have to worry about everything. Where to be, what time, how to get there, do we have the tickets, are we running late, how to address food allergies, etc. It was nice to know all those things were being taken care of by people who knew how to do it and I could just enjoy the amazing things we were seeing/doing. (And I say this as a person who loves to plan vacation itineraries, and does it for fun in my free time. But I also know that travel, particularly international travel, can be stressful.)
3. Special access and skip the line stuff. Again, I think that this is itinerary specific, but for some, there is a lot.
4. The itineraries have been pretty well planned - mixing it up, generally trying to see the best of everything. And they add in a lot of experiences - things that I likely normally would not have done, but which were pretty fun. Like for our Italy trip - pasta making in Tuscany. It was a fun family activity, followed by wine tasting and lunch overlooking the country side. Just a lovely day and one that I would not have planned (as I'm more of a go-go tour guide). Also dinner in the castle and the boat ride at the end of the trip.
5. The itineraries worked for us to do pre-days and post-days mainly as we wanted to.
6. Disney handles the messes. Like when my DD left her phone in the shuttle on the way from the airport to the hotel - we got it back. When the entrance to David get delayed - guides addressed. When we needed bathrooms, the guides figured it out.
Downsides: But not all roses, of course.
1. Cost - I've seen lots of examples of how you could recreate similar experiences for lower costs.
2. Lack of control - flip side of not having to be in control. Again, my thoughts generally on this were to do pre and post days to fill in with extra additional things that you may want to see/do.
3. Food - Food was good, but not great. We aren't foodies, so not a huge issue for us. And we were never hungry.
4. I didn't love everyone on our trip. (But it was possible to avoid those people easily enough.)
There are people who are definitely not group tour people. (For instance, I recall a thread a number of years ago from a man discussing his family's "issues" with the Alaska trip, which seemed to boil down to his DW's inability to go with the flow, and expecting some special treatment versus everyone else.)
Really, only you can determine whether you are group tour people. Good luck.