While it's quite engaging and interesting at first, the glimmer fades in a week or two.
There are a multitude of things you can do as "side quests", as the game follows an extremely nonlinear path. You can manage your town's appearance by planting flowers and trees, catch fish and bugs, do errands for villagers (which are given to you at random), dig up fossils to give to the museum, develop 'friendships' with villagers, compete in tournaments, and of course, quite a few other things to name.
Then there's the multiplayer. Both over Nintendo WFC and Wireless LAN, there's not much lag to be seen; you usually have a lossless and fun experience. In fact, that's where Animal Crossing: Wild World shines at times. There's nothing more satisfying than whacking your friend in the head with a bug net, or digging a pit around him and trapping them at their current location.
Of course, all of these things, as diverse as they are, slowly get more and more repetitive like a bad minigame. It's a big bonus to have lots of friends to play multiplayer with, because you're sure to feel dull by yourself after a week or two.
In conclusion, AC:WW is a great game, provided you're into the concept, just don't expect it to last you too terribly long.