River Song - yes or no overall?
Since it's doubtful she's ever coming back, we are free to discuss whether her character was a success or not, from beginning to end.
Personally I loved her, but mostly because she was played by the marvelous Alex Kingston, one of those actors who's SO good that she can single-handedly improve a weak script. And that should have been on her job description when she was hired, because the only genuinely terrific script she was ever given was the first ("Silence in the Library/Forest of the Dead").