Major spoiler about the ending, so be warned if you have yet to watch this series/the ending and want to experience the disappointment for yourself.

I really can't say that I ever thought this series was actually good, but there was something about it that kept me watching. I like stories with a strange twist and I'm up for a gender-bender adventure.

Let's first go through the main things that I disliked.
The first thing that bothered me is the age difference between the main leads. The FL is from 1986 and the ML from 1998. The ML was like 19 or 20 when the series came out. Him playing this boss like (don't remember his official title) figure of this big company was just not believable for me. But who knows, maybe there are many 19 yo bosses out there and I am just too narrow minded. I'm also not a fan of his acting (except for some moments that I thought were pretty good), maybe because he was still young at the time. He is really handsome, but I would have loved to see more expressions on his face besides o_o.
The second thing that bothered me are how whiny female characters acted. But Cdramas just can't live without them it seems so I wasn't surprised.
The third thing is something I have mixed feelings about; the kissing (of strangers) without consent. I guess it's kinda necessary for a story like this, but in some cases it just made me feel a little uncomfortable.
The fourth thing is the pacing. The series got really draggy at some points and I'm pretty sure this didn't need 24 episodes of 30 minutes. Might have been just me getting impatient and a little bored though.
Fifth; animal abuse. I know, I know, it's just a drama. But poor hamster being carried around (where did he even put the poor thing? In his pocket?) and at some point even being thrown through the air, and that fish being left in a glass of water. My animal loving heart cried for sec.
The last thing I want to mention that I disliked is the worst thing of all; the ending. Why for heaven's sake did she need to get run over? I have no clue what this added to the series except for confusion and frustration. Was there not enough drama or something? She didn't even die. You did this for what?? It also looked ridiculous. The main leads also didn't talk about the FL's "illness". Did the ML even realize what was going on? I feel like he might have figured it out but I would have liked to see that confirmed. Besides that there are more things that didn't get resolved. Were they gonna make a season 2? It's been 3,5 years so I don't think that's gonna happen.

Now on to some positives.
I am satisfied with the FL actress' male look. There were some moments where the makeup was too feminine (like they forgot about it or something) but most of the time it looked pretty good. I also liked the dubbed voice, the voice acting and lip syncing was pretty good imo. Everyone was good looking so no complaints there. Most people showed good or decent acting. The chemistry between the characters was also pretty good. The plot was just interesting enough to keep me watching, although at some point I just binged episodes to get it over with faster. I truly did like the concept of this series, but I would have liked the story a lot more if some things had been done differently. I also liked the special effects used to show the FL's male persona as an actual male. Lastly, I thought the music was nice. Some songs I liked more then others but nothing bothered me.

Do I recommend you watch this?
If you have plenty of time to spare and you're into these kinds of stories then sure why not. Just don't set your expectations too high and don't expect a great and satisfying ending.