As a long time New Balance 1123 wearer, I was interested in seeing how the updated version would feel. The 1123 was one of the only shoes that enabled me to walk without heel and ankle plain. The 1540 does a similar job, but as some have pointed out, the fit is different. It is definitely shorter than the 1123. I would reccomend buying 1/2 size larger if you are moving from the 1123. The toe area is narrower as well, so if the 1123 fits just right, you might consider a bit wider size as well. However, the heel area is the same fit as the 1123, so you may just want to wear the new ones in.
Otherwise, great shoe. It loses a star due to the price increase (and 1 due to the sizing)-why do we have to pay nearly boutique prices for what appears to be a ordinary shoe. Nothing special on the construction.