Good job! Very nice graphics and good execution overall. Some feedback about climbing ladders: if i approach the ladder while holding Up arrow - the character should start climbing automatically as soon as i am near the ladder, so I dont have to press Up again, that would be more intuitive. Also when climbing - the character shouldn't fall off the ladder whe you press Left arrow or Right arrow, only if you press jump or jump + arrow.
Nice idea about adding scrolls with interesting scientific facts :)