I enjoyed watching this show very much, that said it's not as light as I thought it would be, based on the reviews I've read on this site. In fact I think the melodrama tag is completely justified, yes there were no major tragedies, even so there was a melodramatic vibe throughout the entire drama. (melodramatic music, many ppl being perpetually unhappy etc, cinematography)
Song Hye-kyo was really amazing, maybe this was her best acting performance to date. Usually in kdramas I really hate interactions with foreigners, because both the foreign actors (seriously where do they get those ppl?) & the Korean actors speaking English all embarrass themselves so much, that I find it hard to watch, here however the Cuban scenes were surprisingly good. The foreigners spoke English naturally with a normal-ish Spanish accent & our main characters were also speaking like how I would expect a normal Korean to speak English in real life, it was actually believable. The secretary lady & that fat driver were also awesome!

I could go on and on about the positives, but the other reviewers already mentioned all the important points, so I'll just list what I did not like:
1, The ML looked like a female version of Matt Damon. I'm completely used to effeminate looking male Hallyu stars, but this was on another level. (too heavy on the lipstick YO!)
2, There is an insane amount of twisted logic, like that retarded clause ..
3, I didn't like any of the 3 mothers
4, The end of episode 13 was unnecessary & for me that alone made episodes 14 & 15 meaningless fillers.
5, There is that side character that only has one role, which is to recommend that W drink to his coworkers (and to us obviously).
6, The second ML hasn't had a single scene without having teary eyes, I hated his character even without this but ..
7, The ending could've been longer & more satisfying. (still it was ok)