I have to admit I didn't find the first two episodes all that special. But as the show progressed and we could see the characters' struggles and pains, as well as their individual personality, the drama got 100 times better!
The plot is quite simple and predictable but the characters stand out so much that the show just makes sense as it is. I liked every single one of the housemates and Seo Do Hyun (he's such a great person, I am rooting for him). I didn't want to skip any scene when they were together. Their struggles connect them to the viewers and distinguish them from the rest; they're very realistic characters.
The music didn't impress me and, even though I just finished watching this first season, I wouldn't be able to recognise any of the songs if you played them to me. But I don't remember the soundtrack annoying me or anything; it's just irrelevant.
I'm certainly going to be watching the second season!