Transparencies make things less readable. Tap targets are less obvious. Wireframe icons are harder to parse visually. Thin fonts (thankfully larger now) are har

Transparencies make things less readable. Tap targets are less obvious. Wireframe icons are harder to parse visually. Thin fonts (thankfully larger now) are harder to read. Undemarcated areas of UI make it harder to distinguish controls from content (not a feature IMO). I actually like flat design but they've taken it too far.