Apple's stock Photos app has a lot of nicely implemented features and it gets used a lot on my iPhone 6s, but I'm still yearning for the ability to zoom on photos unlimitedly, using the pinch-zoom gesture.
Zooming in Photos isn't possible beyond a certain threshold and that's been ticking me off for quite some time now. Curiously, there appears to be a bug in iOS which overrides this behavior and lets you zoom unlimitedly on a photo.