So the 3/4 night sailings are just to get a taste of what DCL has to offer. I've done them on the Dream and also done the 7 night sailing on the Fantasy (same class), and the overall feeling is very different. With the short sailings, most of the people on board are attacking the activities simular to the WDW minute by minute touring plans. So it feels so rushed. But with the longer sailings, most people relax into the cruise, they take time to breath and aren't rushing around.
The buzz and complaints around the Wish is only because it is new, and soon people will be moving on to the Treasure and then the 3rd ship in the class. If you look at the prices, usually, the 4n on the Wish is priced around 5-7 nights on the other ships.
I did the 7night Western Fantasy cruise for my 40th and it was amazing. There's not enough differences in the DCL ships that I would pick any of them over the itinerary and length.