As a farmer, you can plant flowers and vegetables and trees, and you also can have animals. Like real farmers. You try to earn points by "harvesting" a lot of crops and doing a good job taking care of your farm. The more points you earn, the higher the level you go up, and you can buy more things to put on your farm. In addition to this, you earn ribbons to motivate you to be a better farmer.
Well over time, I've acquired a lot of cats. I used to pile them all together because I thought it was funny, but they started moving around, and now they are taking over my farm. To prove how bad it is, I have recently been awarded the "farmville cat lady" ribbon.