I have to admit by the end I was emotionally invested to the point of crying over the secondary couple. But just because I enjoyed it at some points or I cried doesn't mean I can't be critical of it.

First things first, the female lead was such a generic female character in a romantic film/show. We've seen her a hundred times over, please get rid of this overused rom com dynamic. Her selfishness and her absolute self importance made me continuously pissed off during the entire show.
Second. Let us never overlook the age gap. From the second the 2 leads met I automatically assumed we would watch her grow up and have the romance at a more reasonable age. But that didn't happen. We got a very creepy romance between a man in his 40's (900's) and a 19 year old girl. Her absolute infatuation with him was impossible to get past. How she begged to marry him and demanded love from such an older man made my guts twist.
Truly the show would have been better with the secondary couple as the main. Sunny and Grim Reaper were a more believable pair and ultimately a more tragic story. Sunny was a much better female character. More interesting and overall kept me watching to see it to the end.
The bromance was funny at times and as separate moments they were good but in the context of the scenes they seemed really random and misplaced.

Overall very melodramatic and inconsistent. Inconsistent writing, characters and pacing. It definitely wasn't terrible and certain moments had me go back to rewatch because there were really good individual moments but in the end it seems to be a very cheesy and overhyped due to the handsome actors.

But that's just my opinion