I didn't like Donna at first- she seemed like kind of a pathetic figure, pining for something she couldn't have instead of just living her life.
But after a few episodes, she's grown on me- now my impression is of a strong, smart woman who knew what she wanted and made it happen through patience and determination. She's definitely the first in the new series to be mature enough to confound The Doctor.
I find Donna refreshing after the smitten unrequitted love angles from the previous two companions. She’s there to be “fun”, and I think her character works more often than not. This last Agatha Christie episode was a great ride!
And they actually went through with the Americanization of Life on Mars? Ouch. I have a bad feeling about this. The british version was AWESOME, and I heartily recommend it, especially if you have a love of cliche cop shows which it cleverly parodies. The sci-fi angle is just the cherry on the top.