My first Korean drama was Boys Before Flowers. I had watched Hana Yori Dango and I was reading a forum about it, and people were arguing about if the Korean version was better than the Japanese version, so I watched BBF to compare. I came to the conclusion that both have something that the other one lacks, but both are still great (depending on your preference).
But anyway, BBF didn't really get me hooked on Korean dramas. It just made me realize that Korean dramas existed. What did get me hooked on Korean dramas was Secret Garden (^^)