Although this wasn't the first anime that I had ever laid eyes on, it was the first series that I watched seriously. (I had seen a few episodes of Kanon (2006) the year before but I wasn't particularly interested because I had had to focus on exams). I finished Elfen Lied in one sitting on the day before Christmas Eve in 2007.
After that, I was completely hooked. I was sort of surprised at the same time though because I hadn't expected that anime could be so violent. I had always thought it was supposed to be cute... but what I got was comlpetely different.
After that, I watched The Melancholy of Haruhi Suzumiya on and became totally obsesed with it. (I loved Yuki's seiyuu, Chihara Minori)
Following that came Clannad, though I couldn't finish this until months later because it was stil airing at the time.
I then watched AIR. This is probably the saddest anime I have ever watched (it almost made me cry).
Afterwards came Lucky Star.
For the first five episodes I was thinking how much I would come to hate pure slice of life anime. Konata kept on talking about random things and discussing strange theories and it really put me off, but then I got attached as it improved. I also got excited everytime there was a Haruhi reference.