I completely agree with you. The first two arcs, in terms of story and artwork, were really good. the last two were sloppy, undeveloped and kind of felt rushed. The Mortal Iron Fist arc was a cool concept, but I felt they didn't develop the ideas enough. The last arc was a big let down to me. The end was anticlimactic. I really didn't like the idea of the 8th city being a prison.
Very disappointed if this series doesn't come back in one way or another. I would be interested to see what new powers or techniques Iron Fist learned from the book.