I watched both episodes of this a week or two ago, and they were pretty good. Not your typical documentary you've seen for the past four years. Really gets behind the scenes of what happened and how things progressed from the first World Trade Center to the final attack on Sept. 11th.
Kind of interesting to see how well they've pieced together precisely each terrorist's tracks over the last couple years leading up to the attack.
The second episode was more interesting to me then the first. It dealt more with the final days and the aviation side of the tragedy.