In the first page of this thread, Allyn Gibson has posted the best reply. And while Rose Tyler went off the rails a bit by S2 and was mostly superfluous in the last run of Tennant stories, I'm puzzled why some people really loathed Rose Tyler and call her a slutbag (just because Piper played a high rent hooker in a ITV series).
I still think Season Four had problems and its season finale has not held up well to repeat viewings, comparing NuWho's Season Four to Season One is akin to comparing TNG's Season Seven to Season Three in terms of quality; the later season has more stinkers than the much earlier season that set the standard, but still overall good and has some outstanding classics (like "Parallels" and "Midnight").
I still think Season Four had problems and its season finale has not held up well to repeat viewings, comparing NuWho's Season Four to Season One is akin to comparing TNG's Season Seven to Season Three in terms of quality; the later season has more stinkers than the much earlier season that set the standard, but still overall good and has some outstanding classics (like "Parallels" and "Midnight").