Everything that makes this character interesting and dynamic is pared down so she makes a good mystery, something to fit into Steven Moffat’s puzzle box universe. What’s distressing is that every time he explains a bit of her away, we’re left with the clarified image of a woman who is entirely defined by her relationship to one person, specifically to one man. And while the Doctor does clearly have feelings for River, they are not of the same caliber, not nearly so encompassing. So on top of all this, she’s putting all of her life’s energy (quite literally) into a person who doesn’t focus the same sort of passion on her. It diminishes River, makes her so much less than she seemed in the beginning, an adventurer with her own plans and dreams, someone who the Doctor had to respect and acquiesce to on occasion. Because Gallifrey forbid the Doctor ever has to answer to anyone other than himself. …
Which isn’t to say that there are no affecting moments on the show where River is concerned—it’s quite the opposite, in fact. But those moments are not grounded in any sort of devotion to her continual development as a character. You see the frustration, don’t you? It’s easy to gloss over, to just watch and enjoy, but on more careful inspection you find that nothing means anything. Everything just gets written over for a bigger speech, more tears, another world/universe saved because the Doctor is brilliant and that’s what he does. And the Doctor is brilliant, but so are the people he loves. So are Amy and Rory, so is Craig, so were Sarah Jane and the Brigadier, Rose and Martha and Donna, so is Captain Jack Harness. So is River Song.
So was River Song. But she never quite showed us her real potential. We never got to see her date an android or excavate a lost civilization or save an entire species because the Doctor comes when she calls and no one else.
And that’s the woman I feel cheated out of knowing.