I have been a loyal Brooks Adrenaline product user for approximately 4 years.  The shoes have really worked well for me, my Wife, and Daughter; we all have similar shoe structure needs.  The GTS 12 may look similar to the GTS 11, but it is very different.  The top of the shoe looks and feels similar.  The major changes are with the width and structure of the show.  The width will not impact many people, but for myself and my Daughter, the width changes in the toe box and heel area are deal breakers; we have been using the narrow width in the GTS 11.  The width is significantly wider in both areas for the GTS 12 narrow.  Additionally, the structure of the shoe has changed and you have to really look at the differences between the GTS 11 and the GTS 12 to see them.  I have logged ~80 miles (~20 miles/week) on the GTS 12 and I am giving up on them.

This review might provide some assistance in your own evaluation: [...]