Shattered glass, fell on its edge. I looked into just replacing the digitizer, but removing and gluing back the display appeared too much pain.
You need lots of light and parts are very tiny. Take your time, I would recommend two hours. If you did it before, you can probably do it in half an hour.
Watch the little plastic spacer that is under the metal speaker holder. I took the speaker off, and somehow the little spacer got lost. You can assemble it without the spacer, but the metal holder will be slightly kinked because it presses down where the spacer would go. The spacer must be like a washer that is about half a millimeter thick, and a 1x1 millimeter square.