Other than the bass response issue which was noted later that the inclusion of port plugs would have made a difference on, the only negative thing that was mentioned was some sibilance at high volume. This is something that seems to be consistent from some people's hearing opinions though regarding Axiom as a whole it seems.
I believe the sibilance issue has more to do with the dual tweeters that "some experts" think is not the way to go in speaker design. I have had M80s for awhile now along with many other speakers over the years and I, personally, have never noticed any issue with this. I do have a dead sounding room so I would think it has more to do with acoustics than anything else and as we all know, many of these characteristics get exaggerated because of something someone reads on a website, yet, they personally have never owned or listened to the speakers. The Axiom designs have been around for a long time so in some people's minds perception can become the reality.
It would seem placement and the possible use of the port plugs would tame the bass when placed near a wall so there are options here. It is interesting to note the comments regarding the soundstage. Unlike the bass issue, this is something you can't really alter too much and it looks like the consensus of opinion was that M100s were pretty much superior to everything else that was reviewed.