What I really love about this series so far is the fact that they take the time to build up the entire story and how Moon Dong Eun is going to avenge her past before actually getting to see the revenge and that's truly amazing. That way we can understand better the decisions the she makes.
I just rewatched the drama and as you said the last episodes were very unsatisfying which frustrated me a lot. I got lost multiple times because I couldn't fully understand why the mastermind behind this deadly project suddenly decided to create it and especially where those VIPs come from. Their entrance was horrible to watch and made the drama become somehow plain. However, I had overall a great time watching it thanks to the cast and the cinematography mostly, but also the games which were very intense and the plot which could have been better executed I believe.
Can't wait to see next season!