Hindsight is a beautiful thing, it's ALWAYS 20/20. With that said, I dont think very many of us would have considered Al-Qaeada a viable threat to America before 9-11. I also dont think very many people in our gov't thought Al-Qaeada was a viable threat either. Obviously many of us were wrong about Al-Qaeada.
Clinton had 3 different opportunities to take out bin-Laden but chose not to. If Clinton had chosen differently, this whole thread wouldnt exist. By the time Bush got into office bin-Laden's plan for 9-11 was nearly complete. I dont think we could have found out enough information to stop the attacks in time.
I think the most notable thing done since 9-11 is the greater cooperation amongst all the intelligence agencies. For far to long America's intell services acted more like rivals than team mates. Our Presidents can only act on the information they are given. That information needs to be timely and accurate. I think our intel services are headed in the right direction now.