Art is a form of communication, but beyond that, art communicates more than Ideas and history, it adds a sense of feeling to communication. Art is communication with extra depth added. This could be in the form of paintings, writings, buildings, or anything really. To communicate sorrow, joy, excitement, despair, beauty, love, and the millions shades of all emotions is the noble endeavor art is.
Modern art lacks the ability to communicate well. Modern art enthusiasts would simply respond to this statement by telling me that I just don't get "it". Well, they are right, and that is my point. I am well educated, open, and love going to art museums. If I fail to understand why something hanging in an art museum is art, it isn't because of a lack of something on my part, it is because of a lack of the artists ability to communicate. I am not saying that modern art isn't art, I am saying modern art is bad art because of its inability to communicate.
I recently went to Museum Tinguely in Basel, dedicated to the artwork of Jean Tinguely. He specializes in modern art that moves, so it was a bit more interesting that most modern art museums, but not much. I hope you understand my point in the examples below.
I must add this as an ending. There are a few pieces of modern art that do communicate well. Picasso's Guernica comes to mind as one of these few examples of good modern art. If you are an artist, do not try to be new and different, try to communicate.