To set the tone - we are not cruise people but we did a Mediterranean cruise on Virgin Voyages last fall. It was a lot of fun and we would consider doing another one, maybe for Alaska. Again - we are not really into cruises and we have zero desire to do any of the Caribbean cruises, not even on Virgin. For that, we would just visit any islands individually.
What convinced us to do a Virgin Mediterranean cruise:
1. Europe is a long trip and traveling to only one of the many islands from the US is not really efficient. We were never going to say "Let's travel to Europe and visit Crete or Sardinia" but the cruise allowed us to see many places we never really would have otherwise.
2. Virgin looked to offer a very nice/not cheap experience and it was. We did upgrade to Rockstar status, which removes waiting in any lines and a larger cabin. I totally would suggest it if you can afford it. You also get a personal concierge that takes care of bookings events/other requests as well as access to a less crowded deck area. The "skip to the front of the line" was worth the price alone.
3. No kids under 18 on Virgin are allowed. This is huge and not because we hated kids, but because it changes the atmosphere. There are a lot of adult themed events on Virgin that I believe you do not get on other cruises. This will keep you & your 18 year old kids engaged and entertained while not felling like an amusement park.
4. No buffets - all of the dining is restaurants. Most of them were decent and nothing was awful. It also means there is not a lot of options for snacking, which we liked.
All in all, I would definitely suggest Virgin for anyone without young kids and especially for traveling the Mediterranean.