I thought it was all right, and I kind of expected to dislike it. I had low expectations, but it at least managed to surpass that low bar, haha.
Speaking to that first point about Ki Tan doing nothing, that's not strictly true, and like @lywn said, there is actually revenge, but I can relate to the comment a bit because I was bored with his character through much of the show. He's shown doing basically nothing but masterminding things after a certain point and comes across very static. For that reason, I was way more invested in the bad guys, lol. They were horrible and fun. And also the siblings were entertaining.
I would almost totally disagree with the second point as well. I guess it depends how you view the motivations and actions of Gun Woo, but I was pretty sympathetic to his character (as I think the writing meant viewers to be), so I didn't see the romantic conflict as so cut and dried as that person seems to have seen it. I don't love love triangles, but this one at least made some sense to me. She does care about both of them, and to me she didn't seem stupid for doing so.
All that said, I basically only watched it because I liked most of the cast, especially Jo Bo Ah, and I'll watch anything that Park Ki Woong is in so....I may have been biased from the start, but since those two were basically my favorite characters in the drama (along with Jung Bo Suk and Jin Tae Hyun's characters), I didn't regret finishing it. I gave it 6/10, which for me means it was watchable, but not great. Definitely not bad, though.