I find it hard to say what I like or dislike about paintings. One thing I have noticed, though, is that I find sentimentality embarrassing. Sentimentality I would describe as the too-obvious pulling at the viewer's heartstrings. I want a deeper emotion than that.
A treatment of a subject that is different from what I have seen before always gets my admiration and interest. I don't mean something ugly but more a unique way of seeing. Also I look for the honest commitment of the artist - energy put in, coming from the urgent need or drive to create.