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One thing I can say is that sometimes it is unclear what harmony is fitting with the melody. For example in bar 3 both the left and right hand play a D, so it doesn't sound clear what the chord is (I'm guessing G?). Whereas bar 6, the B and G together show that it is G major resolving into C (which is why two Cs works, as it's clear where the melody/harmony is leading). Its a nice little piece but sometimes can be a bit ambiguous. 

I'm not the best with musical theory so this is just a suggestion and may be wrong ITO theory.

The voice leading rules aren't the only thing in that book. The chord construction ones are also important and there are a lot of tones that function as accented non chord tones when the main tone they embellish is itself a non chord tone. 

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