I second the suggestion to turn off coins - I have a good, not great PC. I have been running the game for a little over 18 hours, and the game only reports 6 hours and 51 minutes.
The same as AquaStarlight - I got to Marston's Gorge, climbed the big steps to the right, and the only thing I found when I jumped was a little rectangle. No gem, no way to finish level, no way to finish game. 1 fight away from the end, and I can't finish game and get the last badge. Hope the developer is paying attention!
Does anyone know if there's a way to go back and play old maps, besides the 7 days displayed within the game? I would love to be able to go back and replay old maps that I either haven't played, or have forgotten about!