See, it's different than any of the other Sims games. It's mostly quest-based, but you can explore the world freely at any time. There's a lot of things to do, really, like leveling up your heroes, getting them married, having a child etc. But, there is a big but. For TS3 players like me (who do not play RPG games and such), it might take some time to get used to the game and its main aspects. For instance, I fell in love with it after playing for two days, but with TS3 it was instant love. I am 14 by the way, and I tried out many RPG games before, didn't like them, but a mix of RPG and Sims turned out really good. For me, it's my second favorite game of all times. But, our tastes may differ. I suggest you watch some videos, read Carl's Medieval Guide, and watch some screenshots, as well. Like Metro said, it's your decision.
EDIT: RunAmok is right. You might get bored with it pretty soon, if you like infinite gameplay. After the first ambition, the same quests are getting repeated quite often, but doing them with different heroes might be interesting. Anyway, after a certain amount of ambitions, the game will finish, so there is an end, after all.