I've only played the first Animal Crossing but what kept me playing was completing my Museum and Bug/Fish lists. I tend to be a completionist so that kept me going. Though I did cheat a bit by fiddling with the date on my Gamecube so that I wouldn't have to play everyday for 8 months to get everything.
As for the new one no I won't be getting it. Partly because I'm never going to own a 3ds and partly because I've moved away from playing those style of games as I grew up. I tried to go back to the original recently but I got bored in an hour or so.