Here in northern Minnesota, the growing season is quite short: it starts late and ends early. Any hearty plant that appears early is appreciated.
Rhubarb is one of those awesome plants that comes back every year. It requires very little upkeep. It's there waiting for you to harvest once it has a chance to grow when the weather warms up.
It contains calcium, vitamin K, manganese, and other good vitamins/minerals/antioxidants/good-for-you-stuffs. Read more about its health properties here and here.