我想是人物性格的刻划。所有的人物都那么生动，即使那些坏家伙也令人难忘。

I think it's the characterization of the people. They are all so interesting, even the bad guys are memorable.

youdao

The remainder of the Republic is, again, devoted to crafting the regime that will produce a distinctive kind of human character, and that of course is why the book is a utopia.

理想国》的往后章节，是全面致力于刻划能催化,独特人类性格的政体，那也当然就是为何此书是本乌托邦。

耶鲁公开课 - 政治哲学导论课程节选