To the left is a link to the Prentice-Hall description of the differences between CMP and CMP2. The effort centers on streamlining investigations, adding new content and bringing more focus. For instance in Comparing and Scaling "the authors have created a number of new problems that more directly convey the mathematical focus they feel is critical. One rather big shift is that the mathematics goals of the unit include more explicit work on forming ratios..." In many units investigations have been removed completely. More actual math has been incorporated as well.
Reading between the lines it appears that developers have recognized and addressed many of the issues and deficiencies noted by Andover students and teachers. The removal of investigations and the compacting of units speaks to the repetition so many students find "boring". The addition of focused mathematic application speaks to the challenge that was missing for some students previously.
It is clear that the program itself had significant room for improvement. Perhaps not quite as robust and rigorous as Andover has been expected to believe.