It really is very similar to the DS version. There are a few nice extras, like the special holidays where you get new furniture, but the core game is still the same. The city aspect is nice, but there really isnt a lot to do there and you'll probably find yourself not bothering with it too much.
I have both. At first, I wasn't going to get the Wii version because I'd played the DS version to death. I was a bit worried that it wouldnt be different enough to keep me interested. I also felt that it was more suited to a portable console due to the need for almost daily maintanance. In the end, I was right, and only played it for a couple of weeks before getting bored. Now I havent switched it on for weeks.