I personally am not excited to see Rose back. I think she has just as much of a right to return as any other companion, but I certainly wouldn't say she has more than any. I thought Rose's ending in Doomsday was heart-breaking and yes, she is the companion that introduced Who to a new generation but that doesn't mean she was necessarily the first companion for many or even the most important for many. She completely overshadowed Martha in series 3 and to an extent Donna in series 4 tbh. Her return at the end of series 4 felt wrong because in many ways it felt shoe-horned in and then she served no real purpose to the story and it felt like she was only there to big up the episode and rehash her emotional ending. As for the former, I can see why they'd do that but the latter was, IMHO, a disaster and ruined for me what made the Doomsday ending so effective. She had a lot of character flaws and not only were these not addressed but to an extent made worse when she returned (and the way she treats Martha is deplorable, considering how Martha's instant reaction isn't childish jealousy but joy for the Doctor). I did however, love her return in the End of Time, I thought that was pitched perfectly.
The difference between Martha's return and Rose's was that Martha's felt consistent with the story and the character. Rose's return and subsequent leaving felt like neither. Whilst we still don't know the exact nature of her return, and I'm sure Moffat will do a good job in accommodating her without it feeling forced, I can't say I'm happy to see her.
