As @CharlieBishop said in her article 20 Rapid-Fire K-drama Reviews "The Heirs: Lee Min Ho is rude to a poor girl (version 3.0) but this time, his weapon of choice is chairs rather than guns".
I just watched it because it's Christmas, I wanted something easy to watch and to see Lee Min Ho in a better shape than Boys over flowers.
My review:
Story: don't lose your time. "The heirs" is "Boys over flowers" with a better hairstyle (and sometimes, but only sometimes, better clothes...).
 The acting: I didn't like Park Shin Hye. She is supposed to be a strong woman, although all the adversities, but she was always crying. Lee Min Ho...pse... but, I liked the evolution of Kim Woo Bin in this show.
 Music: I don't get why they put Love is the moment ALL the time... horrible.
Rewatch value: no, no, no.
Overall: if you have free time, nothing to do, and you want to see something catchy knowing it's not good... this is for you!