Like everyone is saying, since the couple's chemistry was TOO good, the expectation for the story, especially the ending episodes, went TOO high. Consequently, this drama has failed to meet this overwhelming expectation.
First of all, I would like to congratulate the casts and staffs for challenging to make such drama, cause woman-older-than-man couple is a difficult aspect to portray in any kind of stories. The couple has to be well balanced, since if not, the viewers will start to feel uncomfortable. For this drama, the relationship part was absolutely perfect, and the mood created was well matched. I could have given 10/10 just for the couple.
The reason I gave 7.5/10 is not because the story was bad or the ending was unsatisfied, but the maximum I can give was 7.5/10 even the drama had a different ending. As I wrote in the opening, the way this ended could not meet the expectation. Honestly, I cannot exactly explain what the "expectation" was, and unsure what kind of ending could have been good. What I can say is, "Yes, it ended that way, but now it's back at ground zero... They will have to face the same thing again...". Lastly, about the ending, I want to ask others, "So everything was his fault then?"
Other than the ending, the drama had few unsolved issues like the sexual harassment incident and the family problem. It was unclear how those were resolved after all.

Story: As stated above, the directors did really well challenging such a heavy plot.
Acting/Cast: WONDERFUL!!!! Are they dating? One thing to say was... can you please not have such irritating mothers anymore?
Music: Nice, but would have been better if it had more variety and tempo.
Rewatch Value: You can come back to witness their chemistry, but other than that, there's nothing.

Overall: You should watch this drama. I recommend it. HOWEVER, try to suppress your expectation, cause you may end up having a discomfort...