The two main characters were interesting and each had a fleshed background and prominent personality, the male lead was enjoyable to watch since he was unique compared to the usual male lead characters and they were very well acted.

However, compared to them, the side characters were bland and unlikeable to me. I couldn't care less about them.

The story at the start was fun and exciting due to the fact that I was under the impression that it was carefully crafted by the writer, this impression only lasted until about episode 10 when it started to get stretched and therefore losing a lot of quality.
The struggle to fit into the 16 episodes format was very noticeable, they delayed the revelation of the lie the plot revolves around until it wasn't possible to delay anymore. After it was revealed, they pushed weaker plot points to fill in the gap and all interest was lost.

In the end I can't say I totally regret watching it. The show had a lot of potential, if only the filler episodes were cut and the story condensed to about 10 episodes it would be perfect since the premise was good and unique and the acting was excellent. I would've shed some tears if the plot was handled differently because it had the potential to make me.

SPOILERry stuff that bothered me:
Too many silly romance side stories and empty comic relief characters;
Aji 3 went from being completely considered a simple robot under Ji A's control to a being that they adored that went out of her way to save the data of her friend herself and THEN to thing that they ultimately destroyed for some reason and was never mentioned again;
The fact that Min Kyu was unhealthly dependent on Ji A was never solved or mentioned;
The worst offender: the fact that they all believed that he would die if they told the truth just because the other guy died was ridiculous, the circumstances were very different, the very thing he wanted(her being human) was true why would he die? He would be happy instead;
The company chaebol bullshit didn't need to exist;