I try to give 10 when I recognize quality, independent on my taste or how much I enjoyed a drama. Of course, it's an ambitious plan and I fail most of the times, meaning that I end up giving 10 to those I truly liked AND have got quality to offer.
1. SECRET GARDEN. The plot sucked me in from minute 1, it made me laugh like crazy and cry - something I very rarely do. It made me fall in love. It has outstanding acting, beautiful music and wonderful photography, and all the side characters are enjoyable and well chosen, bar none. But it's when I decided to translate the subtitles for a friend that I truly understood why it's my favourite: the script is brilliant. It has so much subtle irony, sarcasm, word puns, insightful thoughts, literary references that translating it was a joy and a very hard work at the same time. Re-reading it made me realize how many things I had missed the first time, in my haste to know what would happen.
2. COFFEE PRINCE. I rewatched this drama recently and liked it just as much as the first time. The acting is so natural I thought it took place in the house next to mine, instead of in the fictional world. This is the drama which made me appreciate Korean shows, because it displays a society so very similar to mine, with normal people facing normal problems. The chemistry between ALL characters is awesome and the way issues like homosexuality, unfaithfulness and true friendship are treated is delicate and hilarious in turn.
3. LIAR GAME. I loved it for reasons which are the exact reverse as Coffee Prince: because it's theatrical. It's over the line, surreal, tremendously clever and addicting. The acting is great too, as over the top as a piece one would watch on stage. Music and general atmosphere are disquieting, and I watched the whole show - 2 seasons and 1 movie - as if I were watching a perfectly staged metaphor of life, with greed, ingenuity, irony, bluff, cinicism and honesty.
Finally, this is a drama which creates questions, instead of answering them. It leaves a wide space open to judgment, which I loved.
P.S. There are dramas out there which I think deserve a 10, but I didn't enjoy enough to bring myself to give them such a high score. One of them is My Name is Kim Sam Soon, objectively a great drama but I never fell in love with these two, such an unconvincing pairing. I confess I didn't find it that hilarious either - embarrassing would suit my feeling better.
Another which is a full 10 in my rational mind is Friend our Legend, but my heart can only take that much. Too heartwrenching, I had to drop it at some point. May take it up again though, because it's absolutely brilliant.
Other dramas I would have liked to give a 10 because I adored them, but don't deserve it, in my opinion, on a cinematographic level. It's the case of the Japanese Long Love Letters, so much I enjoyed it despite its evident failings.