It's always refreshing to see a princess who has better things to do than wait around for a man, and Mulan is one of these. She certainly fits the "girl power" mold, but she tempers this with femininity, love of family, and a true desire to follow her culture's mores of honor. Her relationship with two living parents (rare in the Disney canon) is definitely worth noting, as is her growth as a character.
As one reviewer noted, Mulan's story does revolve to some extent around rebellion against authority. In context, this is somewhat understandable; Mulan had very little choice, but it's worth discussing with kids that her decision was technically disobedient. Battle scenes will be disturbing for young children, as will the dialogue and appearance of the Huns. Judeo-Christian parents may want to discuss the motif of ancestor worship as well. But for those families ready to do so, this is an enjoyable film to watch.