The first thing I notice opening the app is it wants to backup all my photos to the Google cloud. Until last week where there have been consistent issues, I have been a very happy customer of Dropbox for several years; so, I have not been in the market for cloud backups. However, timing is everything and therefore I am excited to have a new option for photo archiving. The price is (incredibly) free for decent quality images at unlimited storage. (You have a limited backup for full quality.)
Secondly, I notice that they have linked previously uploaded images from some various corners of the Google universe, like Hangouts. It was nice to rediscover some photos that I'd sadly long forgotten about in my endlessly growing archive. Below are five shots from my iPhone 4 taken in autumn 2011; these made me smile to see again. Thanks Google!
Thirdly, and finally, they have a playful sort of AI function called Assistant. It collects your photos into automatic slideshows and collages; it makes automatic movies and photo sets; it even edits random images in "stylized" ways. All of this is little (no?) practical use to me as a professional photographer, but in my role as a guy with an iPhone, well, I find it pretty darn fun.
Overall, a very good app with killer potential, if they keep supporting it. Favorite aspect: I enjoy the way I can slide through years at a time. It's definitely a superior experience than the similar Moments view in the regular iOS Photos app. I often feel lost in that view. Here, not so much. It seems more geared to the mobile user, rather than jamming a desktop experience into the phone. (I am really hoping Apple improves all that in iOS 9!)