I have previously played on the DS version of AC, but never bought it. I have the GameCube version and played it for many years. For me, this is a great step up and although much is the same, a lot is different & better.
Positive:
The animals are just like the old characters all AC players know. I like the features of playing hide and seek, which is much different from let say the GameCube version. There appears to MANY different layouts of your own town, as I've visited many other AC players (friends) through the gate feature. All the normal features of fishing, bug catching and special occasions are the same. The post office is bigger compared to the GameCube version likewise with Nook's shop layout as it re-models. It gets you glued to the screen for ages whether it's helping others out, bug catching, item collecting etc. It's much easily with the internet connections to get other fruits and plant them - which is a nice considering it used to take a long time to get them. The graphics themselves are bright, colourful and personally better than other AC games I've played. I love going to town and seeing the items in Gracie's, maybe go to the theatre, getting a new haircut and even getting a balloon sometimes! Red's shop is over priced as usual and as being in a back alley, I find it a creative idea as he is a sneaky character. Oh, not to mention you don't have to wear that daft hat from the GameCube version - also being able to wear many accessories. Being a Wii, I like the feature of being able to turn yourself in your own Mii character. Overall, it's just a good game for old or new players of AC :)
Negative:
The price of the houses has increased largely from what I remember of GameCube - or is that just me? Although the feature of turning yourself into a Mii character, I think it loses some connection to the real AC background. It's really annoying when you enter houses or change rooms, how long it takes to load, a bus comes up at the corner and although it still being a small amount of time, it bothers me greatly. If you're in another person's town and they turn the Wii off, often enough I get the mole outside my house for not saving - so annoying. There's also a lag when in other people's town when you try to e.g. dig which bothers me. The fact other people can chop your tree's down is really annoying and it would be nice to turn that feature off. It seems like you don't create an actual relationship with the animals like in the DS version, and the animals don't seem that bothered about it.
Although the negative points, they're only small things which I've picked out, overall this is highly recommended and will keep you playing for a long time without loss of interest. :)