I think that this becomes one of the central issues of Achebe's work. The idea of "things fall apart" helps to evoke that some of the "bad elements" also "fall apart" in giving way to the new. There is a new order and part of what drives Okonkwo to the level it does is because of the absence of the past. Okonkwo recognizes that what does fall apart is what the village used to be, giving way to the present and potential future. He cannot embrace the reality of what the Western influence has brought into the village in terms of modernization, new access to greater opportunity and the like.
It is in this point where Achebe is suggesting that the entire premise of colonization has to be assessed in a larger frame of reference. When "things fall apart," it also helps to bring out the idea that some of the bad falls out with it. The new vision that Okonkwo and all of the Ibo have to address is a new reality where the past has become transformed. In this world of what has disintegrated, the question becomes how individuals will adapt to this transformative element. I believe that it is to this end that the novel does not make a definitive statement, but rather, like its characters, provides a reality where the reader must assess and apply these principles of adaptation to their own being in the world. It is to this end that I believe that Achebe does not clearly suggest either way that the reality of the Europeans is good or bad, but rather one of adaptation and change.