I will be as honest as possible here. Spoilers ahead.
The show wasn't bad, I enjoyed it for the most part and it wasn't unwatchable. However, there are many things I can critique about it.
Before I get into the negatives, I will say that the CGI and sets for the show are really good. I give it high praise because from my experience, CGI tends to lack in these dystopian Korean Dramas.
These kids are going a couple of days without food and water, running and fighting and show no signs of pain/fatigue?
The reactions of some of the characters seem so unrealistic. Your dad just died and you look like you aren't even sad? Your friend just got eaten by a zombie and there's no reaction? I just feel like the acting could have been better in regards to being more emotional and making it more dramatic.
There were also many parts of the show that did not make sense, for example when the father of On-Jo "sacrificed" himself so that the group could get out of the tennis court. He had more than enough time to get out and close the door. I just don't understand that. This happened for a lot of the characters. I don't mind if they had a plan to kill off a character, but at least do it in a sensible way.
The acting was honestly not good. The only notable actors from this show that were good and natural was Mi-Jin (girl from the bathroom), Gui-nam (the zombie bully), Daesu (the big friend) and the 2 police officers. I really enjoyed the archery/bathroom group and the police officers more because it was nice to watch. The group dynamic was funny, made sense and just worked. Respectfully, I was not a fan of On-Jo's character at ALL. Her acting was extremely corny and honestly hard to watch at times. She had little to no reaction at times where she should have, and overall she seemed awkward. I'm not sure this was the role for her. As for the other leads, they were okay, but nothing special. Nam-ra was a good actor although her character was not well written.
The pacing of the show felt slow as well, I feel like there was little progression in the story line in the first 5 episodes and at times it honestly got boring. I get that they want to stay close to the Webtoon as possible, but I believe it is fine to adapt it to make it better.
Would I recommend this show? Yes, but do not come in having high expectations. I despite my critical review I still enjoyed the show. This is a show you watch if you are extremely bored or do not have anything to watch. Do not expect a cinematic masterpiece.