'Sharing a photo stream is an easy way to keep the important people in your life up to date with your latest photos. Invitees, who must have an iCloud account to join the photo stream, can view, “like,” and comment on your photos from any device set up with Photo Stream. Those invitees without an iCloud account are sent a link to a webpage to view the shared photos; however, they cannot comment on the photos.'
(my emphasis); and from here:
'Invitees who don’t have iCloud accounts can view a shared photo stream only if you enable the Public Website option in your shared photo stream settings.'
As another option, iCloud provides a simple gallery in the form of 'Photo Journal' - uploading of photos from iPhoto to web pages hosted on iCloud, but only from iOS devices; and the photos are compressed to a size adequate for online viewing but are not available in full resolution as with the old MobileMe Gallery. Apple have provided a sample album here.