I would not really recommend this drama unless you are a fan of the main leads, then you could just skip a lot of scenes as I did or just have the time to pass.
SPOILERS
I originally started watching this drama for Seo In Guk. I also went into this drama with high expectations after seeing all the promotions and captivating trailers. It appeared to be a supernatural fantasy romance; my impression assumed it would be something good like Goblin or my love from another star, boy was I wrong! The drama started off as a fantasy rom/com that later reached to become a boring melodrama once the main leads got together. Episodes 1-6 were well written; however, it becomes pretty bad in episodes 7-15. I oddly liked episode 16, extremely cliché with the main leads getting back together, but the entire episode gave off good vibes like the earlier episodes in the drama.
If the writers intended to make the whole drama mediocre like this, it could have been cut to 12 episodes! 16 episodes were soo annoying, like there were so much unnecessary clichés added in the climax like amnesia and on and off breaking up.

PROS:
Seo In Guk and Park Bo Young’s chemistry- what keep me going from dropping the drama! Their chemistry felt so wasted from the bad script written :( I hope they reunite in a better project together!
The comedic brotherly relationship between Myeol Mang and Tak Seon Kyung!
The starting set up of discussing the destruction keeping balance with the good event role played in our world
The main leads cohabitation scenes when the FL discovered that their houses have been merged XD
The cinematography used with the supernatural fantasy scenes.
Seo In Guk’s divine acting expressions playing both Myeol Mang and human- despite the lackluster plot, he can really pull any role he’s given!!

CONS:
The story kept dragging on with long dialogues once the main leads got together- usually in drama for me, it’s supposed to be exciting to see drama couples get together after a long wait. BUT with DAYS, I felt the complete opposite!
I feel like DAYS had so much potential to be a great drama with the concept presented of the balance of destruction and good events placed in our world. I thought the drama would add to that is a better, interesting way. Instead, the drama just focused on the melodrama of the main lead's romance.
In some episodes, I didn't like the FL. I really like seeing Park Bo Young on screen. However, her character was sometimes annoying. A lot of times, she would make decisions on her own without telling Myeol Mang! Examples like breaking up without telling him she's leaving and making both herself and Myeol Mang forget they ever met. Like wtf, why does she not at least communicate any of these problems?!
The second lead love triangle was complete BS and super irrelevant to the drama plotline. I skipped almost all their scenes cause I just couldn't care less. I also hated the SML were close friends going after the same girl ;( If the writers really wanted to do a second lead love story, it could have been added nicely like what Goblin did with AT LEAST no love triangle and was relevant to the plot.
Plain ending- drama kept teasing that the main leads will get married, but what happened to that? At least show a scene where they get engaged :/
Giving no explanation to how Myeol Mang became a doctor as his human career. Are we just going to assume he magically gained all the knowledge from the Deity as well? Like realistically, it takes many years of college and med school for that. As a pre-med student, this was funnier than annoying honesty to me XD
This could have been a 6.5/10, but I’m giving the drama a 7/10. That's me being nice since I'm biased towards Seo In Guk. I hope someday Seo In Guk and Park Bo Young get a better project together in the future to make up for their chemistry wasted in DAYS.