Balanced is related to Level. Level is related to Difficulty. Complexity is a type of Difficulty. Complexity is derived from Complex. 
Nice is the opposite of Sharp. Sharp is similar to Sudden. Sudden is related to Shock. 
Balanced <--RelatedTo--> Level <--RelatedTo--> Difficulty <--IsA-- Complexity --DerivedFrom--> Complex 
Nice <--Antonym--> Sharp <--SimilarTo--> Sudden <--RelatedTo--> Shock 