The web dramas/advertisements are an obvious choice.
I think I'd say Bel Ami where they succeeded in casting IU, Jang Geun Seok and even Han Chaeyoung in lead roles, but the storyline was completely ridiculous. If you think about it, the acting wasn't bad, but the story... (sigh x100000) Read the synopsis. It's just absurd. I watched it for IU but her character was hardly likable too.
K-POP - The Ultimate Audition – this one was trying to ride the tides after You're Beautiful finished airing. The cast, their acting and the characters were so below average that it felt like a production for a school project. I mean I'd support these actors because I don't hate them, but the roles just made them look cheap. The story did have some fun moments but why bother when you have other gender-bender stories that are way better. I'd rather rewatch You're Beautiful a thousand times.
Cinderella and Four Knights – there's an absolute drawback for using the plot that has been used before, in more popular dramas. Why bother? You have those Hana Yori Dango, Hana Kimi, all those Hanas and their other remakes if you really need harem and reverse-harem stories.
Glory Jane – does anyone even know of this drama? Lol. I watched it back then because of Park Minyoung, but please don't torture yourself. I remember it was just gloomy all the time, but not the "cry your eyes out" kind of gloomy either. It was just dull and sidetracked a lot. It's funny to be this bad because this was made by the same director who made Hong Gil Dong, Healer and Queen for Seven Days. Yup, now you see how much this director loves Park Minyoung. I mean, Song Yuri in Hong Gil Dong kinda looked like Park Minyoung as well!
Advertising Genius Lee Tae Baek – Same reasons as Glory Jane, it sidetracked a lot and turned out to be focusing too much on being a melodrama. I thought it would be a romcom.