Oh! Darling is one of the worst Beatles songs ever,I honestly can't stand it.
Even though I completely do not share your view, I understand how you might feel this way.
Give the song a different perspective. I think I know what Paul was trying to accomplish in this song. If you listen to the vocals, Paul was trying to make a belt-em out screaming song. The piano is fairly simplistic. If you listen to at as a "melodic" song, there is not much there. If you imagine yourself in a small club with a singer and just his piano, the performance takes on a different slant.
This is something about many Beatles songs, that I think some people miss. I probably go on about this ad infinitum, but sometimes you have to take a step back. There are works of art that look horrible from one perspective, then when you look from a different angle and know what was going on in the artist's life and what he/she was attempting to communicate, the art takes on new meaning and can become beautiful. This process sometimes requires work.
I probably bored a few people with the above, and you probably didn't even read it.