This review will contain spoilers so just be aware moving forward.

We'll start with Music - way better than S1 due to the fact we didn't have the same song playing almost every episode that sometimes didn't even fit the scene. It was much more minuscule and fitting for this season. 10 out of 10.

Acting/Cast - All were great especially all the returning cast. I mean it's been years since they've last played their characters and all of them seemed to pick back up right where they left off.

Story - Here's where it kind of takes a hit.
For one I know they decided to make their own story away from the web toon which is why the second (and subsequently the third) will feel different but yeah...there are some let downs.
First off there are too many new characters that I really don't give a crap about. Why? Well pretty much the entire remaining main cast returned for this season and the only one to get decent screen time was Eunyu. Moving forward with some spoilers.
The fact that Jisu died so quickly into the season was disappointing. Not to mention the way she died. I know she probably would've died anyway due to what she went through (surgery and post-surgery) but at least make it due to that and not some random kill off. I know this is probably due to Park Gyuyoung receiving more main roles now but it sucks that they couldn't keep her around for another episode or two. It just felt rushed.
I really liked the new army characters (Inhwan & Younghoo) at the beginning but when they focused on them so much alongside Chief Ji I didn't care for them.
I liked Eunyu's story of her looking for Eunhyuk but I was a little disappointed she never commented about looking for Hyunsoo as well. I mean I didn't want a whole ark of that but it would've been nice to know that she didn't just forget about him. Which I know is common sense but come on give us a little easter egg or something that she misses Hyunsoo.
Moving on to Yikyung, her baby becoming a monster makes no sense to me since I thought the monsterization is due to desires. What desires did the baby in her womb have to be born one? Idk maybe I missed some key details I did skip around a bit because you know I came to watch the season 1 characters stories and maybe a few new characters along the way. (I will be re-watching sometime to catch details I missed.) Anyway I feel like they just needed another monster human and felt this was a new unique way to introduce one.
Moving on to Dr. Lim, I didn't mind his character. His character made sense to be added but he also was kinda meh. Also don't ask me what happened near the end during his scenes because I skipped a lot of them to focus on Hyunsoo, Eunyu, and Chanyeong. However, what was unclear to me is is it true that Sangwook/Uimyeong is MH1 or Sangwon? (Again I may have missed some details due to skipping around - it's 4am here and like I need to sleep but I wanted to know what happened.)
Next up, Chanyeong - aka my favorite new addition to the show. I loved every scene with him in it. His character fits right in!
Lastly, Hyunsoo - um...like isn't he the main main character??? Why did it feel like I saw 30 minutes of him in total this entire season??? Disappointing but what little we did get of him, well, after the stone scene was great! I wasn't a fan of his scenes before then because like wtf happened? We get no clear footage of what happened to him when he turned to stone and why he did?
Also back to Sangwook/Uimyeong - what is his problem??? Him and Yikyung's daughter are about to become a force to be reckoned with. And who knows maybe they are father and daughter?
Oh and surprise Lee Dohyun made an appearance as a cliff hanger as Eunhyuk?!? Um, yes...but he low-key seems evil so like...noooo.
Oh and last thing, I don't dislike Yikyung's daughter's storyline and I don't dislike her character. I have a feeling she'll bring a lot to the table in S3 but we'll see.

Long story short - too many new characters that over-shadowed the previous cast. The potential of Jisu's character was cut, Eunyu's shined, Yikyung did all of the just to be killed by her own daughter, dog girl dies off camera granted she wasn't a main-main character but would've liked to see her go, Suyeong dies? it was super sad, Yeongsu becomes an asshole which rightfully so but come on don't take it out on those that care for you, Hyunsoo didn't get near enough screen time, Sangwook's storyline is meh but could get better in S3, the military guys are meh, Chanyeong is *heart eyes*, oh the two randos the one with the crazy girl after Chanyeong and the guy they met early in the season meh, possibly Dohyun/Eunhyuk return/I don't dislike the idea of it. All in all it just felt rushed and all over the place but also I'm too much of a fan of S1 and some of the parts in this season to hate it.

Re-watch value - for now 10/10 because like I skipped some parts. I will have to go back and rewatch.

Overall, I will need to see season 3 and what occurs in it before I accurately say I disliked this season.