I have heard that Investigations is similar to Everyday Math in that it is considered "fuzzy math" in that it de emphasizes memorization of math facts and standard algorithms for problem solving.
My daughter used Everyday Math in grades 1 and 2, and it was absolutely ridiculous. It was beyond easy for her, yet the activities created by the authors were confusing and pointless.
In 3rd grade she moved to a self-contained GT program where they are using the Project M3 program and supplementing with other materials to include other units they wanted to cover.
This has been the first year she is actually learning math and problem solving at school. I have been very happy with the M3 units.
http://www.kendallhunt.com/index.cfm?TKN=7B994979-19B9-B72C-DD0EEE8F1E47D034&PID=219&PGI=246
