I won't call this the best K-drama I have ever watched, but it's not that bad as some people make it out to be. Could the acting have been better? Yes, it could have been because often times you may not be able to connect with Park Seo - Joon , but that's how his character is.
The ending could have been better as the show doesn't tell where and how they ended up. Had those loose ends been tied up, it would've been an A drama.
Still, it's worth watching if you're looking for some period drama action.