I really enjoyed watching this drama.
I started it a bit late (so that I didn't have to wait every week for new episodes) but enjoyed it thoroughly.
It was truly fun and interesting with surprising parts, interesting characters, and good chemistry.

What I loved:
I felt like the whole time-travel bit was quite nicely done (it made me think of Twinkling Watermelon). I always enjoy the Idol-fan trope, so it was very satisfying.
The music was exceptional, and I got really into it (I will definitely add some of the songs to my playlist).
The cast was so good; all the actors did well and had definitive value. They made the drama truly endearing.
I felt like the darker side of the drama was there but not too much and we got to have nice episodes too.
I liked that SunJae waited for the right time to propose and didn't just do what he wanted. The ring appearing was truly magical and sweet.

What I liked a bit less:
I found it disappointing that their first kiss happened when Sol was drunk, and that SunJae knew about it but still confessed and kissed her. I don't get why he was surprised that she didn't have any memories of it afterward.
I feel like the drunk kisses really have to go; they are way too common in K-dramas.
Some technical time-travel parts didn't fully make sense to me, but it's okay.
We still don't really know why the bad guy is a bad guy except that he is a bad guy...
I don't get why SunJae said that he didn't want her to erase his memories again... like, it was to save his life, not a fun little trip for Sol, so... yeah.

Anyhow, I loved this drama. The ending was so fluffy and satisfying; the main leads were cute and fun. I definitely recommend it!