The experience is worlds apart from PE, which is, as the name suggests, just a fancy economy class experience. We pay cash for our UC tickets and still find it to be worth it. The flight becomes a part of the holiday that you look forward to as opposed to a necessary evil to get from A to B. The Gatwick Clubhouse is excellent and many Virgin frequent flyers will tell you that, despite the extra bells and whistles at Heathrow, they prefer Gatwick. The staff will go out of their way to get your holiday off to a good start.
If this is your first UC trip, then make sure you arrive at the Clubhouse at least 2 before your flight to take full advantage of everything. On arrival, go straight to the spa to book your complimentary treatment (do this before doing anything else, as spots fill up fast). Then head to the restaurant, get a glass of bubbly, some breakfast and relax. The menu is breakfast/brunch as Virgin have no late afternoon departures from Gatwick. There are many breakfast cocktails for you to sample.
On board the aircraft, you have a small chance of getting an aircraft without an Upper Class bar on board. One of the Virgin aircraft based at Gatwick had this removed. It also happens to have a much older entertainment system on board (V-Port), which although on-demand, has much less choice than the newer Vera system. That being said, even in Upper Class I find the screen to be poor so prefer using my iPad which is larger and far sharper with better colour.
One of the benefits of the Upper Class seat is that you can dine with a friend or partner. The ottoman opposite you has a seat belt, so someone can join you in your UC suite, even if the seat belt signs come on. Let the crew know you would like to dine together and they will setup your table accordingly. Note that if you are in the first two seats at the front of the aircraft (in the nose cone) these are slightly more compact as the cabin width is smaller, so dining together will not be comfortable if you're in these seats! However, these seats are great for couples despite the fact you can't really dine together.
On the outgoing flight you'll be served a full lunch shortly after take off (starter, main course, dessert and/or cheese+port). About an hour and a half before landing, you'll be served an afternoon tea (scones, sandwiches, cakes). The on board tea selection is really interesting (e.g. 'Turmeric Active' or 'Night Time', which has oat flower, lavender, limeflower and valerian in it), so definitely sample a few of those. On your return flight, which will be a night flight, you'll be served a 3/4 course dinner shortly after take off. The lights will go out to allow you to sleep. When you're ready to sleep, press your call button and ask them to make your bed. Don't be sky about this - they expect you to ask them to do this, as its rather complicated! You will need to exit out of the seat, and this is an ideal opportunity to go to the bathroom and put on your "Sleep Suit" (PJs, which they'll provide you). The seat folds forwards as the back of the seat is actually a memory foam mattress. They will make your bed a sheet, duvet and pillow. They will even have a hot chocolate with marshmallows waiting for you if you ask for one. Again, about an hour and a half before landing, you'll be served a hot breakfast. In UC, you will fill out a "build your own breakfast" card before you go to sleep (you'll find it on your seat when you board), ticking the boxes indicating what you'd like (e.g. bacon, scrambled egg, sausage, brown/red sauce, croissants, juice, tea coffee, etc).
I have flown UC many many times and know it like the back of my hand, so if you have any specific questions, just ask! You'll have a great time and you'll find it a very different experience to PE!