I'm 35 and can definitely say AC is not a "kids" or "girls" title but a great family game. I guess I got into on the Cube sometime the year it came out and many other (guy) gamers my age and in their 20s that I was gaming with online (in PC games) were also into it. Probably the best description a one of my gaming buddies had of it was "digital crack."
Sometimes later at night or on weekends my son and i would spend hours with the game, but for at least 4-5 months after purchase we would boot the game EVERY day when I got home from work and at least catch up the day on it.
The game was the first really ingenious use of real time, where life continued even when the game wasn't running (by reality checking with the GC date/time). You would actually have to plan on certain events. Certain things in the game only happened on Saturday nights, Holidays. Special Events would be set on a date and you would have to boot the game on that do to take part (shame on you cheaters that adjusted the GC clock. You could do it, but the game knew if you jerked with time and scolded you for it when you rebooted it).
My son and I both maintained towns, you could load both town's memory cards and travel into the other person's town. I often scolded my son for going into my town without permission and harvesting the fruit trees leaving me with nothing (selling fruit is how you make cash and once you pick it, it takes a few days to reproduce fruit). Once you visited other towns you would find that people would move from your towns into others never to come back...often writing you a goodbye letter saying that you never came to visit enough or something of the sort.
Over all, extremely addicting. Very non-linear. A goal oriented game only as much as you wanted it to be. Structured very much like the Sims in some ways but not very much like it in others. Not "adult" themed like the Sims, but you still had to build and maintain relationships.
I still occasionally boot the game up to see how the town is doing. When you don't play for a while your house fill up with bugs and the town goes to the dogs and you have to clean it up if you want. Fun addicting game, but not for everyone.