What makes a good photograph?

In my quest to find a reasonably acceptable answer to this difficult question, I picked up a book of Alfred Stieglitz's photographs, thinking to myself, "Okay, let's look at some photographs that pretty much everyone agrees are great and try to pick out what makes them good." Flipping though the grainy, dated images of empty streets and snowy trees, it occurred to me that nothing like this would ever stand the test of criticism in a contemporary gallery. If I took a picture of Manhattan from across the river tomorrow, would anyone consider it art? Doubtful. Stieglitz's photographs are good now because they evoke a certain time for us. They probably meant different things to people when they were first taken, but now they are historical. Goodness is subjective, and the reasons for something being considered good often change over time.

But I'm getting too far out here. In photography, as with all the arts, there is a traditional set of guidelines and expectations for artists to follow in order to produce good work. These can be taught, but anyone genuinely interested in their own work should be able to pick them up organically through trial and error. In the end, a good photograph (for me) is one that makes me stop whatever I'm doing and really concentrate. I don't necessarily have to like a good photo, but it does mean I find something genuinely interesting and engaging about it.