To jump in to your defence: I don't think we were supposed to like River from the start. I feel like she was written a little over the top and annoying on purpose. And just like the Doctor, we didn't know who she was and learned more about her with time. So I think it's absolutely okay to start fully liking her just now. :)
But maybe that's just me. I saw Silence in the Library after the mid-season finale and found it rather tragic and sad, but I think I would've thought "who the fuck is this and why is she acting so importantly?" had I seen that episode before. Funny how things can change from another pov. ;)