We did the 7 day cruise last May and loved it. Personally I don't think you can compare it to staying at a
DVC resort - they are so different, but both great.
We haven't gotten seasick, but two of the nights the boat was rocking and some people were. I would suggest that if you think you might to talk to you doctor beforehand as their are things you can take like the patch etc.
Disney will now offer two different 7 day offerings - one for Eastern and one Western.
The one we went on was the Eastern and had 3 wonderful days at Sea to just relax and enjoy the ship and the spa.
You don't have the room you have at a DVC resort and of course you don't have a kitchen area. What you do have is all your meals included, shows included, movies included, and the ultimate ability to get away from it all.
Add to that the magic of Disney and you have a great vacation.
This may we're doing a little bit of both by taking the 4-day Wonder cruise and then spending a couple days at the Villas of Wilderness Lodge.