Some time ago Google introduced a new website called Takeout where you can download all your data stored by Google at once.

It is enough to go to the Takeout page and select the data you are interested in. For example, unselect everything except Google Photos. Click "Next step" button and wait for an email with a link to your download. I got my link after 2-3 minutes. The link takes you to a zip package containing all the data you requested.