[side note:
A little surprised at the justification of many of the negative reviews of this, but then again, the audience is probably going to be in the realm of a) kdrama fans b) koreaboos c) simply fans of IU's conventional beauty d) fans of IU's music (which I would like to say carry more intellect than other kpop fans, but..) and whatnot... Basically, these reviews are so shallow. You don't have to bloody understand everything you watch? Is there no one over the age of like 13 watching this?
I can understand negative reviews because of poor acting or plot, dadadada. But some people don't bother thinking for two seconds about what they're watching. I'm just noticing many reviewers glossing over the complexities and depth that I feel should be appreciated. Of course, I'm also only exposed to English reviewers, let alone to those written on the internet.]

I enjoyed what this collection of works was trying to do, some more than others, but all in all appreciated the layers and complexities of depth provided, that of which I am still ruminating on-- the best kinds of fiction does this, crawls around your head for days following. If I'm honest, my appreciation for the works is partly with the fact that it is created by Korean production in mind, and I'm sorry if that comes across as condescending in any way. I am glad IU was the one to take on this project.
I'd say a downfall of the project would be how short each of them are, because they couldn't really expand on what they were discussing but had a lot of potential to evoke thought and leave a lasting impression, had they'd been longer. The storylines (mostly No 1) were appropriate for the time constraint, but (2,3,4) somehow wanted to be more than its 20-30 minute form, if that makes sense.
Overall, they were far from perfect, but I can appreciate the intent and experimentation.

I really enjoyed the second one's ambiguity and mystery. I interpreted as a kind of discussion about society's superficiality, especially regarding modern 'romance', but also regarding femininity, female power dynamics, gender tropes. I love the way satire is used, I felt it was quite effective within the plot, given the time limitations. I think the characters had an interesting dimensionality to them, especially the male who I really identified with-- The insight into the workings of his mind was very very intriguing and raw, which I appreciated, especially in the Korean cinema scene, (this is hard to articulate--the concepts themselves are very abstract) but I loved the way it really captured the visceral way that the mind 'thinks'. Also the insecurity. The insanity. The vulnerability, rawness and foolishness that humans feel but hide from others. This one was more brave and not afraid to confront but was more serious. I liked that it didn't try so hard to be artsy-indie like 1 and 4 (or, more-so 4).
But beyond its meaning it was thrilling to watch. Not sure if it was intended but i felt it had a Charlie Kaufman influence to it, also reminded me a bit of Punch Drunk Love in some of the scenes inside the man's head.
I liked this one the most not just because it fit my taste but also because it had intention while still being interesting, and also was "unconventional" without relying on this to appeal or sacrificing the story.

I like how the first one left so much up to a kind of unsaid narrative, while using the game of tennis to make inferences to a story beyond the camera. The relationship between Doona and IU was pretty engaging and left me wondering what their history was. IU plays the naively strong sense of self that adolescents tend to have very nicely, which I only came to appreciate after the episode was over (seeing her other performances) because I initially read it as not-the-best acting. My bad.
Some things were vague, and I enjoy ambiguity to some extent, but there were times when it was a bit unnecessary or overdone. Like the ball placing into IU's hand or certain expressions they shared. I don't like things being spelt out to me, but some of it wasn't even trying to suggest anything, leaving it a bit abstract. When fiction pieces try to pull off this ambiguity, it is usually clear that this is what they are going for. But in this one I wasn't too sure whether it was trying to rely on subtext or just lacking substantial context. Nonetheless, I did enjoy trying to figure this one out and develop a hypothesis about it, which I believe is what interesting texts do, so I appreciate that.

I'm gonna skip the third one because I while I can appreciate it, I think it was pretty kdrama-esque and didn't stand out to me personally because I'm not into the "pop" genre(?) of kdrama-- so my comments would naturally be biased.

The fourth was what I was the most disappointed in. While the third I didn't have any expectation for after grasping its general premise and genre, this one I did, because I'm the most drawn to its themes and genre. While I do remember enjoying some aspects of this one, these unfortunately didn't remain in my memory long enough for me to comment on, ha. I don't even think I can articulate my thoughts on why I was disappointed in this one. I think the character and themes suited IU the most and yet the part was very lacking in substance. It felt very pseudo-intellectual to me. It tried but didn't deliver enough depth in my opinion, given its topics. I like what it tried to do very much, but I get this feeling that the scriptwriter/director didn't even fully grasp their own message/intentions. I think IU did better than them.
I'm sorry this isn't very specific, it's honestly because I can't remember the part very well but can only remember my reaction. I will definitely watch again to really come to terms with my thoughts on it and the messages better.

I feel like if I were to sum up my thoughts it would be: like what it tried to do, but didn't quite deliver to utmost potentials. Not that I'm expecting it to be perfect, just that it was a bit ambitious in its messages but failed to grasp the weight and complexity of them.