Purists complain that the cubist effect of steep hillsides dotted with square, flat-roofed houses has been spoiled by modern development, but the beaches all around are still pleasant.
The hillsides remain untouched but, the beaches have become polluted, disgusting, and ruined. 
mnli hypothesis: The hillsides remain untouched but, the beaches have become polluted, disgusting, and ruined.  premise: Purists complain that the cubist effect of steep hillsides dotted with square, flat-roofed houses has been spoiled by modern development, but the beaches all around are still pleasant.