I enjoy this type of game. I do prefer the ones with fewer differences and the ones that change a found difference to match the real picture. But honestly, I haven't found one of these in which the order you find a difference matters - the markers don't prevent you from finding all of the differences. You've done a great job with that.
Probably just a rounding thing, but mine says Total = game avg. (80) + time modifier (83). But my total is shown as 162, not 163 as the formula implies.
Lots of fun! It's kind of frustrating though when one guy has no problem crossing a bridge but another gets stuck on the transition from the same bridge to the land.