Who here understands what a door frame standing on its own in the middle of the room tries to convey to the viewer?
Just because you see nothing in a work of art, that don't make it so, laddie.
I could go on for hours about all the possible interpretations of a doorframe in the middle of a room, starting with the conventional concept of surrealist distortion of context (a door's rightful place is surely at the edges of rooms, along the walls); through the more postmodern concept of challenging the viewer with art that can be viewed as well as experienced (one can look at the doorframe, but one can also walk through it); and finally ending up in the new-agie naughties, talk about the spiritual implications of doorways in general and seemingly useless doorways in particular.
I'm not going to invest the effort, however, because in my experience, self appointed "critics" of modern art are not satisified with anything less that a clear cut and unambiguous purpose to the work, which, I'm afraid, takes things out of the realm of art and into that of engineering.