The rating depends on three areas: Cleanliness, Abundant Nature, and Abundant Living
Cleanliness means:
1) less than 10 weeds
2) less than 10 items on the ground (not counting sea shells, fruit, mushrooms, flowers, buried fossils, buried gyroids, buried Pitfall Seeds)
3) no garbage (Empty Can, Boot, Old Tire, Spoiled Turnips)
4) no Rafflesia
Abundant Nature means:
1) appropriate number of trees (I dont know the counts yet)
2) many flowers
3) high Nature Points from Public Works
Good: Flower Clock, Flower Bed, Flower Arch, Wisteria Pergola, Straw Fence, topiaries, Solar Panels, Wind Power Generator, Windmill
Bad: Garbage Can, Jumbo Monitor, Oil Excavator, Tire Play Equipment, Picnic Sheet, Traffic Light, illumination items, Tower
Abundant Living means:
1) high Living Points from Public Works
Best: Campground
Good: bridges, benches, outside lights, Garden Chair, Hot Spring, Fire Hydrant, Stadium Lights, Solar Panels, Lighthouse
OK: almost everything else including Water Well, Fountain, clocks, Signboard, Face Board, signs, art, monuments, etc.
Bad: Garbage Can