First of all I am a bit disappointed because the opening credit spoiled a bit some of the characters personalities so I recommend to skip it especially for the first half eisodes...
This drama combined fantasy, mystery and romance very nicely! Time traveling is a really difficult trope because relativity can dig really big holes, but this show didn't fail and ended up to have his own uniqueness, even tho it has frequently used themes.
I really loved the male lead performance, he was able to differentiate the past and future self with only his acting, even tho they're the same character they are different and you can tell. There was also some hilarious parts (especially in the beginning) and some very romantic (the scene on the stair was very natural and I found myself giggling when she answered his confession through his past self.)
The mystery was good, I predicted some things (in part because of the op) but still really enjoyable, I didn't felt the urge to finish it (it happens frequently that I get bored in the second half of many dramas unfortunately)
Also no annoying music effects or jingles repeated infinitely, the opening song is quite good