This is a Trip Report from the Upper Class cabin
Ground Staff
Food & Drink
Entertainment
Seat
Cabin Crew
So this was my first DTCI - great experience, arrived 5 mins after opening due to my excellent driver timing the run perfectly (we don't use Virgin ever - due to being outside the VS Car's range - and on a Z here anyhow, so not eligible). My driver liked it, I liked it, into security lane inside 60 seconds, and baggage checked to destination, - the DL hop was on same PNR, but was paid direct to DL, not via VS due to VS directly not offering it with no availability. I liked the fact VS seems to automatically link the flights despite being booked/paid for serperately. (Noting one leg is even being paid personally as a personal extension to a work trip).
Security was not a breeze however, as the 2nd customer of day, I got a good going over, I think in order to diswade me from getting to clubhouse before staff ready, as I was not the only person suffering. Total time was 10-15 mins at security, making me thankful for the private lane - and having 2 security staff to my bag of wires (working in IT, this is my toolbag). I may ship it next time

Arrived Clubhouse as they opened still though as pax #3 due to the security delays - to have breakfast, full english. Ended up with breakfast envy at the chap next doors scambled egg/salmon, which seemed a better option in every regard. A champers, a redhead, and a "surprise me" drink followed, which was a kind of blackberry drink, which was excellent.
Onto plane ahead of first call, but after the E/PE had loaded, as the clubhouse was busy as UC was fully booked, and I wanted to get in my seat to setup my stuff. Walked straight on plane in seat, champers and paper.
As soon as entertainment system booted, I gave a AAA to passenger next door for his Bose QC15's(I have same, and hope to be repaid in kind when my bose's run out by another VS pax!).
Plane in UC had 2 semi-recognizable D-list celebs, my wife would have known who, but my rubbish pop knowledge just let me know they had been on the telly - and were likely pop stars (one male one female). Staff on plane noticeably did pander to these pax more. Bar was empty all flight, and I could not remedy this myself as had to drive on arrival at final destination. They were both quite nice though to the other pax, which was a surprise given my experiences on similar flights in past on other carriers.
Food/Drink service on route was excellent - however the Beef food ( I had read reviews but didn't fancy the alternatives) was super tough compared to the meal I had on BA WTP on last trip. The little touches on the meal, and the starter did beat BA, but the main really let the customer dissapointed.
The 2nd meal was the usual sandwich cart. I don't eat egg sandwich so asked to avoid, which was catered for - however the rest of the sandwiches were quite quite stale. BA seem to manage non-stale sandwiches, but VS on last 2 flights have been noticeably stale.
Upon landing, PE bags came off ahead of several UC pax, including myself and the male celeb's. However once thorough an empty JFK immigration and empty customs/security check for transit, it was off to T2 I think it was for the internal DL hop on a bus. A long bus ride, and upon arrival was not impressed. T2 is horrid, and looks worse than Indian airports! Off to skyclub when my transatantic VS hop allowed access. Food awful, drink awful (non alchoholic), coffee acceptable, and at least the wifi was fast. Overall it is the worst AA/DL club I've been in though (I have access to them all courtesy of amex plat) - but as mentioned at least had wifi for the 2 hours I had to wait.
Note to customers transiting, you have to use the VS baggage re-check desk, NOT the DL one currently - who helpfully point you in the VS direction and apologise for the non-integreated systems - they did mention my flight had moved and gave directions to the new gate. The VS desk however - This only has ONE agent, who was helpful if surly, and wasn't no-where near as nice as agents in London. The boarding card given ahead of security by VS in London however was useless - I would recommend going to the Delta "help" desks to get it reprinted with a boarding zone, as the staff in the skyclub who were not helpful at all in this regard. I mentioned in UC and then showed pass to DL agent - who gave an instant personal exit row allocation and first group boarding with first class pax. They couldn't upgrade me at time, I didn't ask, but she offered.... (but would have for free) if it wasn't for weight issues. The internal flight was great - 15 people on entire plane that sat 75... and first was quite full, so they wanted to put people at rear to make weight distribution better. Quick 2.5 hour hop to BNA and down.
Overall for my first VS->DL on one PNR post merger trip, it was acceptable - and will mean more business to VS in future for me at least if this is usual acceptance. The Delta agents outside the SkyClub were very helpful and nice, and actually better than the VS equivalent I ran into at JFK.
Next hop is a "small" 6 ish hour internal routing on a weekend of about 2.5K miles from BNA-LAS via LAX on DL. Fun, but at least it's scheduled on an airbus, not a CRJ.