We don't all hear the same. For instance, I really don't like harsh, treble filled headphones so for me, a gentler top end is a bonus.
For example, I love the Senn HD650 sound and the HD600. The Bose isn't the be all of high definition, but it is a pleasant listen that many people find impressive on first hearing. It is definitely not sibilant for sure. It has a very strong bass which has been referred to in the reviews that have appeared on this site and it has been stated as being overwhelming and muddy. To some extent, that can be overcome with an amp. (Just like the Senn 650 can shine with certain amps)
I just don't like to see wholesale damning of something because everyone agrees. Before long, it all becomes the truth whereas some people are perfectly happy with their Bose headphones.
I use them sometimes myself and I don't find them un unpleasant listen and we ought to be a little more careful sometimes about how we say things and describe things. Derogatory remarks do nothing except (I suppose) make people laugh which is not so funny when you do it back to the very people that start it.
Anyway, I've been having a bit of fun with this just making a few sweeping little statements of my own. Soon, they'll all be true as well.
In all honesty, they are not the best but reports of them are exaggerated.
Ian