I am a long time user of Flickr, but I have been cross-posting images to Google Photos. I am also starting to go through my old machines and storage media to find other photos I can load to Photos. I originally uploaded my best images to Flickr so there were many images available that had not been stored in the cloud. You get old and you begin thinking about passing photos on to friends and family.
Google Photos does not store images in the original quality as captured by a high-end camera unless you pay for storage. At this point, I do not. Photos has some other very interesting characteristics. It works on images you upload to offer you things you may not bother to explore on your own. It edits images in different ways. It combines sequences of images to create simple videos. It creates slideshows and photo books.
The feature that I find most fascinating is various ways in which I can search my thousands and thousands of photos. Traditionally search would require that I add tags to my own images. Some tags such as location might be added by a camera phone that stores such metadata. This is not how Photos works. It finds ways to identify the images and does a surprisingly good job.
I encourage you to create a corpus of images and try various searches yourself.
For example, I know I have an image of the arch from Saint Louis. As a demonstration, I asked Google for photos I had taken in Saint Louis. The arch was located even though this image was not tagged in any way. I remember taking this photo and thought there were other images I tool near the site of the arch. Sometimes such images would also be returned. Not in this case.