I fly very regulary with them in UC, so I am probably not the person to answer this question. Why? well, there is a great difference between your first, second, third UC flight to your 20th or 30th flight
After a while, you start to notice the niggly things that on first flight you would not see.
I will try to be objective.
The high points
1) Dedicated check in at LGW/MAN, Downtown Disney special check in line so no queuing.
2) If flying from LHR/LGW the Clubhouses. No one flying to Orlando has anything like them. Hot & Cold All you can eat food, free computer access, library, cinema, TV room, games room, unlimited bar, Shoeshine guy, Hairdressers, jaccuizi, spa, massage room, nail and other girly bits repair.
If you are flying from Gatwick, get there as soon as they open 07:00, to make the most of this pleasure.
3) The cabin. As has been said many times, once you have turned left, you won't want to do anything else. 14 seats (though their are rumours of more seats being fitted in the lGW aircraft) in your own personal cabin, and it feels like you are on your own small plane as you will have at least two dedicated FA's for your cabin (until you go for a walk into the inhumanity of Economy) the decorations are very nice, the bar which you can sit at is a joy, the seats themselves are an experiance, nothing like it in the world, taking off whilst having your seat reclined.
V-Port avaible ATM only on LHR aircraft is excellent, the screens on LGW/MAN aircraft nice and large, your own personal space is great and when turned into a bed is surreal.
4) the service and food/drinks availability are OK, the food served on china plates on trays is better than economy/PE food and you get to choose from a menu card and fill in your order (on the way back, you choose tyour many choices for breakfast as well) Good wine selection.
5) The Pijamas. You will be handed out some PJ's to change into. these are yours to keep and are hard wearing and very usefull

6) The amienity kit, a canvass shoe bag with bits and pieces including Cowshed beauty products, toothpaste and brush, eye cover, Virgin metal pen, Pair of socks, ear plugs, polo mints, razors, shaving cream, moisturiser and lip balm. If you are travelling with kids, they will get this kit plus the KiD satchel.
7) the revivals lounge. Get back to LGW and have a shower and breakfast before journeying home
The "down side"
As I have said, this has to be purley objective as for many peoples first UC flight they would not know or notice:
1) LGW plane boarding. The scrum outside the boarding room is a mess. You as a UC or AU passenger have the right to enter the room by a seperate queue, but this never happens and people think you are just pushing in.
MCO is much better, a seperate queue with a red carpet, nice.
2) The reduction in items in UC. The flowers on the bar have gone, the red sating seat pillows have gone, the choice of wines has reduced.
3) The food is not as nice as it used to be and less choices
4) The damned ameinity kit. This used to be a superb Molton Brown kit, went through last year a pathetic cardboard sleeve and they are, due to the amount of complaints, starting to get their act together again.
5) The use of the UC toilets by other passengers.
6) The lack of V-Port on LGW flights
7) On the flight back, the "rush" by the FA's to get everyone fed and asleep.
8) The lounge at Orlando, not being a Virgin clubhouse, means that its not the same at all, no food and no food allowed in.
9) the way that the seats/cabin are showing wear and tear already.
10) And my biggest bugbear CONSISTANCY! One flight can be totally different to the next due to the crew loaded.
BUT and this is a big BUT, regardless of my little whinges, and they are minor, there is nothing like it for such a long journey.
What class are you flying out in? the differences will be massive.
ENJOY!!