Much like many people who watched the entire season, I was hooked like no other after season 1. The way they were all stuck in a small space and the dynamics between all of the characters were very well done, it felt like they explored the side characters as well as the main characters which I appreciated. They continue to do this throughout all of the seasons which I really like in a show, especially seeing them grow (if they don't die first).
The amount of deaths is actually ridiculous, but I had a love-hate relationship with it. It was sad to see so many people I adored go, but it would make no sense to have everyone live until the end. It would have nullified the stakes and made it easy to predict in that way. It did, however, do the opposite...After a while I was certain that almost nobody would make it, you could just feel that they were going to either kill or monsterize almost everyone the audience grew attached to except for the "main main" players (and even some of those!!).

Definitely much better than season 2 since it leaned back into the monster-verse of it all while incorporating less of the military (still included, but more intertwined) which I wasn't as interested in. Everything felt much more connected, and I found it very easy to watch all at once. Acting was great, especially Song Kang! Hyun Su's growth as a character is really cool to see in comparison to the first season. Absolutely loved the dynamic between Hyun Su and Eun-Hyuk. It was very similar to the first season, but different enough considering the change in their characters. The way they bicker (kind of like brothers in some instances) really made me feel warm and fuzzy because it was a happy circle back to season 1.

I simultaneously liked and disliked the final battle scene with Nam Sang Won. It felt less like a physical battle to see who was strong, but more of a mental one. I think it makes sense though considering that's what the entire series is about if you think about it. It was just a little surprising since there was constant talk about who was stronger. Ends up having a really cool interpretation because you could say that, due to Sang Wook coming back and actually putting an end to Sang won, humans are actually the strongest. Very cool way to think about it.

Eun-yu made me sad though. I was really looking forward to seeing Hyun Su have somebody he could actually hold onto considering he's lost so much, as have all of them. Eun-yu came so far in the way she cared for people and put others before herself as opposed to season 1, so to kind of see that go down the drain was a little disappointing. There was the assumption that she would get there though, considering Eun- Hyuk did, so it's not too bad, I just would have liked to see it myself.

Overall, I would 100% watch the series if I hadn't watched it before, and I would probably rewatch season 1 (as I have already while waiting for season 2), but not the rest of the seasons. If you see the ending of the series once, that's really all you need, but I'd say it's worth it to get there.
Watching the ending was bittersweet, but the beginning is always a ride.