I think that after six months (or there about) I'm still something of a newbie; "of all time" doesn't mean the same for me as for those of you who have wtached j-dramas for years, obviously! It has been interesting to read this thread to see what people's favourites are. I have seen (and agree with) some of the choices, but there are also many that seem popular that I haven't watched yet. Some of them are already on my PTW list.
So far, my favourites are Kimi wa petto and Orange Days!
I also really liked:
Rich Man, Poor Woman
Gokusen (s 1)
Mitsu no aji
Hana Yori Dango
Bambino!
The Tempest
Last Cinderella
Liar Game (I've only seen the first season so far)
So far, Kimi wa petto has been the drama that made me react the strongest, emotionally, because I felt that I could relate to Sumire in so many ways. (I mean the way she feels about herself and her place in the world, etc.) And the relationship between her and Momo was interesting and (probably?) unique. Also, I think you'd have to be made of stone if you're not moved by Momo's cuteness.
But I loved Orange Days almost as much. It's very different from Kwp, so comparsion is a bit unfair, but I found the characters and story very captivating and likeable. It made me very happy to discover a drama like this.
Rich Man, Poor Woman was the first j-drama I watched, and I was surprised that I liked it so much. It made me fall hard for j-drama, love at first sight. I should probably re-watch it in a year or two, to see how I feel about it with more to compare it with.
It was when I watched Hana Yori Dango (the fourth or fifth drama I watched) that I realized I had become a drama addict, because I finished it really quickly and barely wanted to go to sleep... I have mixed feelings about it, though. It was a... seductive drama I guess; it pulled me in almost from the first moment and I watched it obsessively, I laughed out loud sometimes and even talked to the cats, and when I had finished both seasons, I was sad that it was over. But there were also many things I found annoying and stupid with it. I don't think I want to re-watch it, because I'm afraid I wouldn't like it as much the second time. (It was not this drama that taught me to appreciate MatsuJun.) I wonder if I'm the only one who has this kind of mixed feelings about HYD...
I'm going to watch the rest of the Liar Game series sometime, because I really enjoyed it. I like this kind of drama a lot, even though most of the j-dramas I've watched so far has been romance!