This just goes to show how people watch films and pay attention to things differently. David was one of the most clear and obvious characters to understand in the film for me. The heart and heartlessness of his character were telegraphed in the first 20 minutes of the film. I thought they went out of their way to make his perspective on humans, his creator, and their creators very obvious, which explains his motives and every action he made in the film. There are so many details packed into the film regarding him I could write an essay on it.
It seems you did not care for the film, but I invite you to watch it again just for that performance, because if you missed it, you missed something special.
The only question open with him are what his motives are with helping Shaw at the end, and this should be up for interpretation. I know exactly what I think he has on his mind at the end, but in every other part of the film, it SHOWS you what is on his mind by his actions and reactions the the various characters.