Doctor Donna was my favorite Doctor of the last three. Not my favorite companion, but that short time she was Doctor Donna was brilliant. It also led to the second saddest companion leaving story I’ve seen. How horrible to not remember any of it.
I completely agree that she was great in the sudden role transfer and that her memories being erased for her to survive was a very sad development, but Donna at some point, had already started to grow on me and I came to like her as a companion.
I also liked Martha Jones and wished she had appeared as a straightforward companion rather than going back and forth to Torchwood. I think that is why I didn't care so much for Donna at first, that along with her vacuous babbling.