I have to agree the plot is not that varied. The scene did revolved around office, apartment and certain other places.
Acting wise, Im si wan is really awesome. He managed to pull the character really really well. Her girlfriend also did good.
BUT, i think lee dong wook could do a slightly better job when maintaining his facial expression and voice when speaking. Ngl but sometimes he looks sly carrying that psychopath character hahaha. Overall terrific show.