This is really good drama, quite complex and amazing acting from greatest actor Jo In Sung, others were good too. many things are different from classic romance-melodramas, I mean it shows not fairy tale but reality and real characters.
though it should be shorter, I think 12-14 episodes would be good, because many situations are repetitive and even makes it boring in the middle - in the beginning story catches you, ending is bomb too, but most episodes are drugged, but you can't skip because there are many emotional scenes (though repetitive), so it would be much effective drama with interesting start, emotional development and bomb like (perfect) ending if it was shorter.

about Jo In Sung's character: this character would be absolutely unlikable if not acting of Jo In Sung - he wasn't bad guy we all like, wasn't good hero we all cheer, wasn't smart/badass/capable character we all admire, wasn't that kind dramaland classic CEO/rich guy who is attractive... he had nothing to like but Jo In Sung is real god of acting that made this pathetic weak not smart character star of the show....

SPOILERS about ending:
I like the tragic fact, it was perfect fit, Jo In Sung is amazing brilliant actor and I watched it because of him... BUT the whole drama build up natural chemistry between FL and SML, it was obvious that she loved him, though we could feel very sorry for ML (Jo In Sung) it was understandable why she fall in love for second guy. ML really loved her, had everything to give her... but somehow he was misfortunate and it's realistic when some people want to do right thing but their actions become opposite, so she fall for SML not ML...
Also ML's obsession and what he does in the end is understandable and great ending...
I just don't understand last dialogue between FL and SML... after everything she is in good place, with man she wanted, without problems, and all of a sudden she understands that she isn't happy with him and loves other guy? WTF? I can understand if she loved both, maybe more SML (it was obvious from her actions and expressions through all story) but in some way she fall for ML too, loving 2 men same time is rare in movies and maybe never was in kdramas but it's quite realistic and I would like if any drama has courage to show that... But even if she understood that loves/feels sorry for other guy too, it couldn't make her unhappy with the man she loved so long and wanting to leave him (and goo again in same repetitive, hard , impossible situation where she suffered so long) ...

p.s. she was ice cold to ML all the time he loved her like crazy and then says "I love you" when was killed by him in another man's bed? .....