I like it! But it is much more expensive steel and the number of belts you go through along with the time it takes to polish is really going to drive up the price of a knife made from M4.
When we work with the M4, we can really tell a difference in the wear resistance of the steel over CPM S30V or CPM 3V. I have heard people complain about how hard it is to sharpen D2 and CPM S30V....CPM M4 is definitely not for them. This is steel that it will be easier to keep sharp than to resharpen when it gets dull. Diamond stones will do it though. I haven't found any knife steel yet that they wouldn't turn into a grey smear.
All that being said, I don't think it is the blade steel for everyone or every knife. But it is good at what it does.