I used to like the old Windows photo viewer thing on Win7, but the one in Win10 is just ugly in my opinion. Completely without soul or charm. Like many new "modern" designs, it comes across as clinical and uncomfortable.
I've heard rumors that it essentially sends snapshots of what you're viewing to Windows HQ, along with all the other stuff they want to keep a record of, but I frankly don't know if that's true. While privacy is a concern of mine, I don't particularly care if someone finds out about the staggering amount of adult art I've accumulated over the years.
I'd really just like something that's a bit different.