I just returned from a DY longhaul itinerary in premium economy and was very pleasantly surprised. Flights were on time - we left a half an hour late from MCO but arrived a half an hour early in CPH nevertheless.
Crew was pleasant and efficient; aircraft was clean, spacious and airy; food was acceptable for airline E+ food (no worse than most and better than some other airlines). In fact the breakfast before landing was quite nice - smoked salmon with capers, sliced tomatoes and red onion, a warm bagel with cream cheese, coffee, juice, water and multiple offers of refills. We did not eat the dinner opting to try to sleep since the flight left MCO at 11 pm. I can't remember what the daytime lunch meal was from CPH-MCO but remember I found it quite acceptable.
I booked discount premium outbound and premium flex on the return because I thought we might need to change our return flight. Sure enough, we had to delay our return by two weeks and it was very easy - just a few mouseclicks - to change the flight to the same one two weeks later with -0- change in fare and no change fee.
We were permitted 2 checked bags each, maximum 20 kg each. On the return, we checked 3 bags rather than our allowed 4 but one was 23 kg which they let go without a fuss (no overweight charge), and one was an oversize SKB guitar case and we were also not charged extra. Our carry-ons were not weighed - we both had rollaboards (we were within the allowed limits anyway if they had checked), plus I carried a small backpack in lieu of a purse as the extra personal item. No issues either in CPH or MCO.
I was dreading this flight and have avoided trying DY since they rolled out longhaul but their itinerary was just too good this time since it allowed us a direct flight from CPH-MCO in under 10 hours outbound, 8 1/4 hours on the return. All other options require a connection (EWR, IAD, ORD, FRA, KEF) that is never pleasant and drags out the travel time to upwards of 16 hours.
My only complaint is no lie-flat option seats but the premium economy seats are quite wide and pitch is excellent (46). By comparison, a similar fare for this itinerary is Icelandair's Saga class and their Saga seats have less pitch (40 to DY's 46), although I might give their service a very slight edge (e.g. no amenity kit on DY; blanket but no pillow), but again that requires a connection in KEF.
The cabin of the 787 is far superior to FI's old 757's. SK's updated Economy Extra is also quite nice - superior service and food to DY at a similar price point - but seats have less pitch (38) and our itinerary requires clearing immigration and connecting at EWR, IAD or ORD which I prefer to avoid.
I would not be pleased if I were on one of those flights with the 48+ hour delays and hope they've sorted out those problems (although I've been stuck mid-trip in connecting cities overnight with both SK and LH and and both were a nightmare despite being in business class both times). But for our inaugural DY trip, we were satisfied.