Photos on Google has changed from Picassa to Google Photos, but the features are quite lacking. In particular if you want to download a bunch of picts or all of them for the matter, there seem to be no solution.
Here comes Google Takeout to the rescue: https://takeout.google.com/settings/takeout
With Takeout select whole albums, or the entire Google Photo content and download away!
From the menu, all your data is available to download. Neat.