The Fusion gets better reliability ratings than the Toyota Camry and Honda Accord. To be compared to those cars, that is a huge deal considering how much their owners love them and care for them.
I don't own a Fusion, but would really love to. I would need to drive the 4 and 6 cylinder to see which one I'd like more, but I would probably choose the I4. I don't drive much each day, so the better gas mileage (29 hwy) would be a plus for me. The power difference might feel really good though in the V6, so I would reccommend that you try both models.
Incentives should be really good too. Stop in to a dealership and take a look at them. I think you'll be impressed.
And thanks for supporting an American company.