I'm the opposite. I like Donna, but think there is some sensible building to a logical ending for her. Ignoring all the spoilers, speculation etc from what we've seen so far she clearly is adult enough to challenge the Doctor on his stances. She saved some Romans against the Doctor's wishes and that was probably for the best, but she killed the wasp, I think, against his wishes and that was less good. But neither time was there any consequences. She's to my mind facing a microcosm of the Doctor's dilemma of playing God and that means ultimately she must face a big choice and the consequences. And that must be her death to save others, or cop-out alternate reality/mindwipe to not scare the kiddies too much.