All the customization options. I love being able to change my furniture colors. Even though a lot of us end up with similar sets, it can all have a different feel depending on the coloring we chose. Plus, more options for the mayors is always a bonus, a lot more options now than in the past.
I look forward to seeing if the next day brings me a hybrid!
I'm also fond of decorating my town and houses (mules as well). But I love interacting with my villagers, listening to all the cute things they tell me.
I love observing the villagers when they are outside. I just follow them around and watch them be quirky. Mostly Chrissy, she is always making me smile.