I had the Guide 4 before purchasing these shoes and this is what I'm basing my comparison on.  So far I've only had a couple runs in them, but here at the things I've noticed so far.  These shoes are lighter than my Guide 4s.  The construction is very similar and is comfortable.  I did replace the insoles with some orange super feet, which was the same set-up I had in the Guide 4s.  The insole the in the Guide 6 seemed to have more cushioning that the previous generations, and a bit better contour to your foot, but they felt akward since I was used to the super feet.  The orange "Vizipro" color is definitely bright and gets people's attention.  However, it has seemed to dull a bit since a couple runs (road dust?).  Overall I'm happy with this purchase, and look to get a good year of running out of them.