Official Apple Feedback link for Photos

As of OS X 10.10.3 the new Photos app is bundled with Yosemite.

As a completely new application, users who have been familiar with iPhoto or Aperture are likely to find significant differences in workflow and new ways of organising photos should they wish to use Photos rather than continue with the older apps.

Apple provides several dedicated feedback links to allow users to provide specific feedback on products/software - for Photos a specific link was unavailable on release, but this has recently gone live:

https://www.apple.com/feedback/photos.html

Not quite sure exactly when it appeared, but thanks to:

Mr. Apple101

for posting it in a recent thread.