I honestly don't mind expies or harems, as long as they are done correctly. Notice in a harem anime, a character doesn't end up with all the people within the harem, just one. Or in School Days case, the character does sleep with everyone and then learns his lesson by getting killed in the end.
Expies are okay as long as the narration does not say "Sue has the same hair cut like Sailor Moon's but blue and has the same outfit as Lara Croft in the Tomb Raider Series and has eyes like Itachi Uchiha." Instead what you cold say (not that I want this character to ever exist) "Sue has long blue hair that goes down to the floor tied into two long ponytails with bright red eyes, who wore a dirty periwinkle tank top and brown cargo pants.