Combination of factors makes for a thoroughly enjoyable watch: 1.) Great acting by very capable actors makes you laugh during funny moments and immerse during emotional scenes 2.) The production value (sets, camera work, art direction) is very high, great quality and has obviously been designed with lots of care - loaded with artistic shots and a feast for the eyes 3.) Script is well written - has good combo of comedy, suspense, plot discovery, touching romance (as with all shows, there are ups and downs with slower phases during the 40 episodes but this does not detract from the overall feel the creators are striving to evoke) 4.) Plot/themes - particularly liked the focus on what genuine/true love means (not the angsty/immature/ revenge type theme that seems too common in many c-dramas) , family, empowerment of women, at times ingenious use of the shapeshifting plot for good laughs, logical plot that explains itself