In short:
* photos lose some metadata including GPS
* You will lose your RAW images (AFAIK)
* videos are always transcoded with a lossy conversion
I've walked into the same trap. I'll probably use Google Takeout to hopefully recover my own data and treat Google Photos as an ephemeral destination from now on.
This is what I've found as well. Although Google Takeout is strictly better than pulling your files down via their API, even the metadata in takeouts can be mucked with.
I'd strongly recommend only using Google Photos as what it is: a _lossy_ backup (that gets expensive if you have a big library).
If you care about your originals, use one of the several applications that allow your phone to backup your originals directly to your server (either at home or that you're renting). Here's a list of apps that do this:
