They're very different. Harvest moon is a farming simulator. Animal Crossing is a "hanging out in a small village" simulator. You don't have a job. You just log in each day and see what's happening. There's only so much to do per day and the time is based on the real world clock. So if you want to plant flowers, you have to wait three real days for them to grow. It's a game you play for a few minutes per day over the course of years, rather than one where you play for 40 hours in the first few weeks until you beat it.